Access 2010 Invoicing

I have a database with a monthly income table with 3 different categories of accounts - Research, State and Outside. I need all records with the account type called “Outside” to be given an individual invoice number, and that number can’t be repeated from month to month. Then I need to save that information in another table to keep track of payments and such (an invoice history table, for example). Is there an easy way to do that? Thanks!