VBA to produce a unique and incremented order number in col A

I am looking for a way in VBA to enter a unique order number value I.E. DHOrd000x or VndOrd000x into the first blank cell in column A. I already have the code to enter in the rest of the order values, just looking for a way to generate a unique order number when submitting the order onto the sheet. The code for the submission I have now is...

Private Sub Save_Click()
          
       lastrow = Range("C" & Rows.Count).End(xlUp).Row

        Range("B" & lastrow + 1).Value = TTNum.Text
        Range("C" & lastrow + 1).Value = Req.Text
        Range("D" & lastrow + 1).Value = ReqD.Text
        Range("F" & lastrow + 1).Value = DH.Text
        Range("G" & lastrow + 1).Value = DHNum.Text
        Range("H" & lastrow + 1).Value = DHCst.Text
        Range("R" & lastrow + 1).Value = Rsn.Text

          MsgBox "One record written to Sheet1"

          response = MsgBox("Do you want to enter another record?", _
              vbYesNo)

          If response = vbYes Then
              Req.Text = ""
              ReqD.Text = ""
              DHNum.Text = ""

              Req.SetFocus

          Else
              Unload Me
          End If

End Sub

Can this be done in code? Any help is greatly appreciated, thank you.