Working Macro not auto updating

Hello All, and thanks for any feedback. This is in Excel 2013

I have the following Macro in my workbook which does exactly what it is suppose to do when I run the macro,
but it does not run on it's own like it suppose to do??? What did I do wrong here?

Sub Worksheet_Change()
Application.ScreenUpdating = False
    ActiveWorkbook.Worksheets("Clients").Sort.SortFields.Clear
    ActiveWorkbook.Worksheets("Clients").Sort.SortFields.Add Key:=Range("L2:L100" _
        ), SortOn:=xlSortOnValues, Order:=xlAscending, CustomOrder:="YES,NO", _
        DataOption:=xlSortNormal
    ActiveWorkbook.Worksheets("Clients").Sort.SortFields.Add Key:=Range("C2:C100" _
        ), SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal
    With ActiveWorkbook.Worksheets("Clients").Sort
        .SetRange Range("A1:L100")
        .Header = xlYes
        .MatchCase = False
        .Orientation = xlTopToBottom
        .SortMethod = xlPinYin
        .Apply
    End With
    Application.ScreenUpdating = True
End Sub

Thanks for any input