Sub InsertNewWorksheetAndName()
Application.ScreenUpdating = False
Dim nowMonth As Long, nowYear As Long
nowMonth = Month(Now) - 1: nowYear = Year(Now)
With ActiveWorkbook
  .Sheets.Add After:=Worksheets(.Worksheets.Count)
  .Sheets(.Worksheets.Count).Name = nowYear & "-" & Format(nowMonth, "00")
End With
Application.ScreenUpdating = True
End Sub