Sub Try_This()

    Dim strFilename As String, D As Workbook
    Dim newWeekNo As String, newWeekStart As String

Set D = ActiveWorkbook

newWeekNo = Range("sWeekNo") + 1
newWeekStart = Format(Range("sWeekStart") + 7, "d-mmm-yy")

strFilename = D.Path & "\GJCT Roster Week " & newWeekNo & " WS " & newWeekStart & ".xlsm"

D.SaveCopyAs Filename:=strFilename

Workbooks.Open (strFilename)

Range("sWeekNo") = newWeekNo
Range("sWeekStart") = newWeekStart

D.Close

End Sub