I'm 26 and went through college without every drinking at a party. In fact, the only alcohol I ever had in college, my mother bought for me--I think I may have had about
three shots worth out of that bottle of sake over the course of two years.
Personally, I don't like the taste of alcohol and have never drank it on that account. When I would be offered alcohol at a party, I simply told people, "I don't drink." Everyone was fine with it (I am woman, though). I didn't get kicked out for being a party pooper or anything. This included both social functions in the U.S. and in Wales, so being okay with not drinking isn't just limited to people on U.S. campuses. Although, I think you will find being at a party sober where the entire intent is to get s--t faced is pretty boring. In fact, you look around and wonder why anyone wants to get drunk; they all look like idiots. Not to mention getting drunk makes normal people have diarrhea and/or vomit; it can only be 10 times (or more) worse for you.
I have been at gatherings with friends in recent years where the intent was to have a good time and talk and getting drunk just sort of happened. Those are good parties to be at since people talked and told stories and didn't get so drunk they couldn't stand-up straight; you can still have a good time sober around moderately-drunk people because it's all about the conversation and interaction, not about the booze.
My suggestion to you would be to simply tell people you don't drink. If they try and pressure you into it, admit that you have a health problem that prevents you from drinking. You'll probably find other people with health problems that keep them from drinking too (people who have sezuires can't drink, nor can most diabetics--gravitate towards the tee-totalers for a better time socially).
If you're in a frat house or something where you feel you need to keep up appearances, bring your own "drinks" to the party. I.e. orange juice without vodka, caffiene free cokes without whiskey, non-alcoholic "wine" coolers, virgin pina coladas, that sort of thing. You can even make tea that looks like beer (minus the head). A few beer empty beer bottles with tea and cleverly re-capped and no one will ever know. Of course, you can always show up a bit after the party's started, get yourself a beer and walk around all night without drinking any of it. No one will ever notice, especially after they've had a few.
Not only will your stomach thank you for not drinking, but you never have to worry about getting so drunk you wake up in bed with someone and wonder how you got there or what you GOT from them! That and designated drivers become really popular on a drinking campus, lol.