Help in Paging Through paged data source class...

Hi to all,
i am making a web application in which user logged in,,after log in they can see their personal messages by clicking the inbox hyperlink.. i have a grid in inbox.aspx which shows messages only belong to that specific log in person..at 1st page data shows because i pass his/her username in querystring and then use that username to fetch data from database and bind gridview with it..i m doing paging with it through "Paged Data Source Class."..at first page data shows 10 records, but if record is more than 10 then,  when i click the next hyperlink btn i recieve an error that query requiers parameter username which was not supplied..
kindly help me that how can i pass username after each request when next hyperlink btn clicked and fetch data from specific username and bind it with grid,,

Thanks in advance..