AJAX does not work, it does not paint fullcalendar

Hello, good afternoon, classmates, I have a problem with my ajax code, what happens is that when calling my function drawnCalendar () since c # executes well, it even enters the function's success but I can not make it paint fullcalendar the weird thing is that he paints it only once when he starts the page I know that success works because I have sent alerts and shows them without inconvenience.

 <%@ Page Title="Kardex" Language="C#" MasterPageFile="~/Master.master" AutoEventWireup="true" CodeFile="Kardex.aspx.cs" Inherits="Kardex" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
    <script type="text/javascript" src="scripts/jquery.js"></script>
    <script type="text/javascript" src="scripts/alertify.js"></script>
    <link rel="stylesheet" href="css/alertify.core.css" />
    <link rel="stylesheet" href="css/alertify.default.css" />
    <link rel="stylesheet" href="css/estilos.css" />
    <link rel="Stylesheet" href="plugins/ui/jquery-ui.css" />

    <link rel="stylesheet" href="plugins/fullcalendar/fullcalendar.min.css"/>

    <script type="text/javascript" src="plugins/ui/jquery-1.9.1.js"></script>
    <script type="text/javascript" src="plugins/ui/jquery-ui.js"></script>

    <script type="text/javascript" src="plugins/fullcalendar/moment.js"></script>
    <script type="text/javascript" src="plugins/fullcalendar/fullcalendar.min.js"></script>

    <style type="text/css">
        table select { font-size:11px !important; padding:0 !important }

        table {font-size:11.5px}                       
    </style>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"> <section class="content-header">
          <h1>
            Empleado
          </h1>
          </section>
                <!-- Main content -->
                <section class="content">
                  <div class="row">
                    <!-- left column -->
                    <div class="col-md-12">
                      <!-- general form elements -->
                      <div class="box box-primary">
                        <div class="box-header with-border">
                          <h3 class="box-title">Kardex Empleados</h3>
                            <div class="pull-right">
                            <asp:Label ID="lblTotal" runat="server" Font-Bold="true"></asp:Label>
                            </div><!-- /.pull-right -->
                        </div><!-- /.box-header -->
                        <!-- form start -->
                          <div class="box-body">
                                <div class="row">
                                    <div class="col-md-2">
                                        <div class="form-group">
                                          <label for="exampleInputEmail1">Número de Empleado</label>
                                           <asp:TextBox ID="txtNumEmpleado" runat="server" CssClass="form-control" MaxLength="5"
                                                AutoComplete="off"
                                                                AutoPostBack="true" >
                                           </asp:TextBox>
                                           <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ErrorMessage="(*) Campo Requerido"
                                                ForeColor="Red" ControlToValidate="txtNumEmpleado" ValidationGroup="vg_reporte">
                                           </asp:RequiredFieldValidator>
                                        </div>    
                                    </div>
                                    <div class="col-md-3">
                                        <div class="form-group">
                                          <br />
                                           <asp:Button ID="btnBuscar" runat="server" Text="Buscar" 
                                                CssClass="btn btn-primary" ValidationGroup="vg_reporte" onclick="btnBuscar_Click" 
                                                ></asp:Button>
                                        </div>    
                                    </div>

                                    <div class="col-md-3 pull-right">
                                     <asp:LinkButton ID="btnExcel" runat="server" CssClass="btn btn-success" >
                                            <i class="fa fa-file-excel-o"></i> Descarga Excel
                                        </asp:LinkButton>
                                </div>

                                </div>
                                <div class="row">
                                    <div class="col-md-12">
                                        <div id="calendar">

                                        </div>

                                        <div class="box-body table-responsive no-padding">
                                        <asp:GridView ID="gvKardex" runat="server" CssClass="table table-bordered table-striped" GridLines="None" 
                                            EmptyDataText="Sin información"
                                        >
                                        </asp:GridView>
                                        </div>
                                    </div>
                                </div>
                          </div><!-- /.box-body -->

                          <div class="box-footer">

                          </div>

                      </div><!-- /.box -->
                      </div>
                      </div> 
                </section>


<script>

    //AJAX

    function drawCalendar() {
        $.ajax({
            type: "POST",
            contentType: "application/json",
            data: "{}",
            url: "Kardex.aspx/MyMethod",
            dataType: "json",
            async: "true",
            cache: "false",
            success: function (data) {
                //eventos = data.d;
                //alert(JSON.stringify(data.d));
                //drawCalendar(data.d);

                $('div[id*=calendar]').fullCalendar({
                    header: {
                        left: 'prev,next today',
                        /*left : '',*/
                        center: 'title',
                        /*right: ''*/
                        right: 'month,agendaWeek,agendaDay'
                    },
                    editable: true,
                    events: $.map(data.d, function (item, i) {
                        var event = new Object();
                        event.start = item.start;
                        event.title = item.title;
                        return event;
                    }),
                    loading: function (bool) {
                        if (bool) $('.loading').show();
                        else $('.loading').hide();
                    }
                });
            },
            error: function (XMLHttpRequest, textStatus, errorThrown) {
                debugger;
                alert("ERROR: " + JSON.stringify(XMLHttpRequest));
            }
        });
    }
</script>

</asp:Content>

My code in C #

static IList events = new List<Event>();
 protected void btnBuscar_Click(object sender, EventArgs e)
    {
        buscar();
    }

    public void buscar()
    {
        try
        {
             //Ejecuto Procedimiento Almacenado

                while (lector.Read() == true)
                {
                    if (lector["Concepto 1"].ToString() != "")
                    {
                        events.Add(new Event
                        {
                            title = lector["Concepto 1"].ToString(),

                            start = lector["Fecha"].ToString(),
                            backgroundColor = "#f56954",
                            borderColor = "#f56954"
                        });
                    }
                }
                con.Close();
        }
        catch (Exception ex)
        {
            excepciones(ex.Message.ToString());
        }
    }
[WebMethod]
    public static IList MyMethod()
    {
        try
        {
            //Do here server event  
            IList eventos = new List<Event>();

            eventos = events;

            return events;
        }
        catch (Exception)
        {
            throw;
        }
    }