I'm running a Lenovo X61 which i carry around my college for getting on the internet at various points in the day. The network has always been finicky but recently it's gotten worse. I'll connect using iwconfig, get an ip from dhcpcd and log in using vpnc to their system. Sometimes I'll stay connected for hours but most of the time within 30 seconds my network traffic will drop to zero and i'll be unable to do anything. My computer still belives it's connected, however to try again i need to put my wireless interface down, put it back up and try again. It's gotten so bad that i've got a window on my computer pinging yahoo or google constantly in order to know if i'm still able to get online. I know other people who have used Arch Linux that don't have the same problems as well as people who use Ubuntu who haven't had any problems either. It seems like my computer is a special case. Does anyone have any suggestions on how to fix it? dmesg doesn't show anything out of the ordinary going on and i don't know where else to look for errors or other things to try.

Edit: this doesn't happen on my home network. It's a problem that only happens at school.