change last cell in column

Well another question, thanks to mudraker I have this code

Sub Workbook_Open()
     
   Dim sWS As String
   Dim sMonths As Variant

   Select Case Day(Now())
   Case 1 To 5
      sMonths = Array("January", "February", "March", _
         "April", "May", "June", "July", "August", _
         "September", "October", "November", "December")
      sWS = sMonths(Month(Now()) - 1)
      Sheets(sWS).Range("b38").value = Sheets(sWS).Range("b38").value
   End Select
End Sub

It works great for what i want to do except the cell b38 will not always be b38 it will however be the last cell in column b. any ideas?