lastrow problem

Hi
I am using the following code to write rows in an excel workbook,the problem is that after adding a row using this code, lastrow remain the same so each time I want to add a row,the code add it to the same location
What's wrong?

VB Code:

Set wkbSource = Workbooks.Open("C:\test\test.xls")
 
Set oXLSheet = wkbSource.Worksheets("Stat")
 
sKey = InputBox("Enter the name of the Key that u want to add", "KeyManagement")
 
lastRow = oXLSheet.UsedRange.End(xlDown).Row
    j = lastRow + 1
    
oXLSheet.Cells(j, 1).Value = sKey
oXLSheet.Cells(j, 2).Formula = "=SUMPRODUCT(COUNTIF(INDIRECT(" & Chr(34) & "'Sheet1'!L2 : L1000" & Chr(34) & ")," & Chr(34) & "*" & sKey & "*" & Chr(34) & "))"
oXLSheet.Cells(j, 3).Formula= "=SUMPRODUCT(COUNTIF(INDIRECT(" & Chr(34) & "'Sheet2'!L2 : L1000" & Chr(34) & ")," & Chr(34) & "*" & sKey & "*" & Chr(34) & "))"
oXLSheet.Cells(j, 4).Formula= "=SUMPRODUCT(COUNTIF(INDIRECT(" & Chr(34) & "'Sheet3'!L2 : L1000" & Chr(34) & ")," & Chr(34) & "*" & sKey & "*" & Chr(34) & "))"

thanks in advance