returning to the same page after log in

Hello all! This is a bit difficult to explain. On a site I am building I sometimes use the GET method to forward values to the next page. There are certain pages that you need to be logged in to to be able to see data. So you arrive at the page, you realize that you are not logged in, so you type your username/password and hit 'log in'. Then the page gets severely messed up as the GET data are not forwarded (at least, I think that's the problem). Any ideas how to solve this? I tried to send a header("location: ...") with the document_root and request_uri as the location, but that doesn't do the trick.