Try this following function to get 3 char format type of month:

Function Get3CharMonth(ByVal pMonth As Integer)
Dim mStringMonth As String
Dim mMonth As String
mStringMonth = "JanFebMarAprMeiJunJulAgsSepOktNovDes"
mMonth = Mid(mStringMonth, pMonth * 3 - 2, 3)
Get3CharMonth = mMonth
End Function