VBA Help to Sort Worksheets

I have a workbook that I a having difficulty in sorting the worksheets. I want to sort the sheets starting after sheet 3 which is called "Master". I had it working where it sorted it first time that I ran the macro but the when a new sheet was inserted after the Master sheet then the sort all went wrong.
Here's the current code and I have attached an example workbook. Would appreciate some help

Sub Sort_Worksheets()

Dim N As Integer
Dim M As Integer
Dim FirstWSToSort As Integer
Dim LastWSToSort As Integer
Dim SortDescending As Boolean

SortDescending = True   'Lower Nearest Left
'SortDescending = False 'Higest Nearest Left


If ActiveWindow.SelectedSheets.Count = 1 Then
    FirstWSToSort = 4 'Start Sort at this sheet
    LastWSToSort = Worksheets.Count
Else
    With ActiveWindow.SelectedSheets
        For N = 2 To .Count
            If .Item(N - 1).Index <> .Item(N).Index - 1 Then
                MsgBox "You cannot sort non-adjacent sheets"
                Exit Sub
            End If
        Next N
        FirstWSToSort = .Item(1).Index
        LastWSToSort = .Item(.Count).Index
     End With
End If

For M = FirstWSToSort To LastWSToSort
    For N = M To LastWSToSort
        If SortDescending = True Then
            If UCase(Worksheets(N).Name) > UCase(Worksheets(M).Name) Then
                Worksheets(N).Move Before:=Worksheets(M)
            End If
        Else
            If UCase(Worksheets(N).Name) < UCase(Worksheets(M).Name) Then
               Worksheets(N).Move Before:=Worksheets(M)
            End If
        End If
     Next N
Next M
'
Sheets("Register").Select

End Sub