Sort, Filter and then auto number sequentially

Dear All

I'm doing my accounts spreadsheet and although lots of you have helped me in the past - to which I am greatly in debt!! There is another problem, that i would like your help on:

As I do the accounts at the end of the week - I input data randomly e.g. data for Thursday may be inputted before data for Monday. Which is no problem in it's own right; but the cash exp has to have a sequential number i.e. PCV1, PCV2, PCV3 etc based on correct date order.

The attached worksheet sample: I've recorded a macro that will:

1. sort by date order
2. filter cash exp

Now how do I get excel to automatically fill in the sequential numbers i.e. PCV1, PCV2, PCV3 etc?? Because at the moment I do this manually.