What I usually do in this case, is that I have a table called tblUserProfile that has the information for all of the users of the database (including their username, and group). When the database is opened, have a hidden form open that check the CURRENTUSER contant to find out who has just logged on, and contains all of their information. By keeping this form open all of the time, you can refer back to this information at any time in your code or queries.
Note: This can only be done in a Frontend/Backend database.