Why am i banned when i didnt use bf3 tweaker ?

Are you banned on all servers ? Or just that one ? - Or do you just keep getting kicked by punkbuster ?

First thing to do is update your punkbuster first.

You can do that here: http://www.evenbalance.com/index.php?page=pbsetup.php

If you are banned for real the best thing you can do is contact them

More info to find here, perhaps you can find some answers:

http://www.pbbans.com/appeal-ban.html

and if you got really banned just look for your ID and ask for a ban appeal..