Find last cell in named ranges and insert a new row

[inarbeth]

I am creating a worksheet in which the user will use a Userform to insert additional items which are either credits or debits which will be placed on an underlying worksheet. I have two dynamic named ranges, Credits and Debits. Credits starts as A6:D6. Debits starts as A12:C12. When and if the user adds items, I want the new item to go into the first empty row in the relevant range and for a new row to be inserted immediately below the new data. Users may add no items or may add many. They may also go back and insert items on a "second pass" through the document. I have data (totals and other stuff) below the ranges in columns A, B, C and D, so I cannot use

Dim iRow As Long
iRow = ws.Cells.Find(What:="*", SearchOrder:=xlRows, _
    SearchDirection:=xlPrevious, LookIn:=xlValues).Row + 1

to find the last row as that finds the last row in the whole sheet and inserts the data there.
I use

 ws.Cells(iRow, 1).Value = Me.txtCreditDescription.Value
ws.Cells(iRow, 4).Value = Me.txtCreditAmount.Value

to add the Credit items and

 ws.Cells(iRow, 1).Value = Me.txtDebitDescription.Value
ws.Cells(iRow, 3).Value = Me.txtDebitAmount.Value

to add the Debit items.
How do I find the last row in the expanding named ranges and insert a row there so that the data in it becomes part of the relevant range?

 

[inarbeth]

Bump. Can anyone assist with this please? Another way of describing what I am doing is to use the Userform to add data to the row above the last row in the range and then to insert a new row below that row.