I'm pretty shocked to hear this, because the non-drinking student is becoming a staple of university life. I know four teetotallers. Two for medical reasons,and two out of preference. (these two will have the occasional drink.)
I find that it's best not to make a big deal of not drinking, and still go out, and chat to people. If the people outcast you, then they're rubbish friends, and I'd say that it'd be best to find some new friends.
There are some groups at my university that have a heavy drinking culture. I find it odd that you are more pressured to drink in the hockey club than in the real ale society, (who will always accept non-drinkers who prefer pubs to clubs) but I guess things are weird.
Most universities have policies that state that non-drinkers are not be made to feel unwelcome by corridoor reps. I certainly know that lancaster does. Maybe you should see what your union's policy is.