When I first went to orientation last year, I felt like it was summer camp. I really HATE that feeling of feeling like a total douche when everyone seems to have already "found" each other. I was going to school with a guy who was already a good friend of mine, so we hung out together during orientation. He's the biggest social butterfly on the planet so he would go over and talk to people and I would stand there like a *****. It was funny, in my small class (former class, to be accurate) all the Muslims found each other, the Mormons found each other, the married people found each other (mostly Mormons), people with kids found each other, Asians found each other, all within like 20 minutes. The people I ended up hanging out with were the ones who went to a sportsbar duing orientation and got drunk and then came back to orientation blitzed. Those are my kind of people...
Anyway, it did take awhile to find our "group" but eventually we did. And there are DEFINETLY cliques, no two ways about it. We all sat in the same part of the room (the back), went to the same places, went out to dinner, etc. We hardly ever saw the other groups socially. It's really weird when you think about it. Can't imagine living in a dorm with my classmates. I would have jumped out the goddamned window within a week. You're with the same people ALL THE TIME. Yikes.
Point is, it takes awhile to find your groove, but you will find it. And it is tough to make friends with chicks, no doubt about it. My best friend from med school ended up being a chick, but that's only because she has a very "male" mentality and she and I are two peas in a pod. Find some cool guys to hang out with and screw the bitchy chicks in your class.
Good luck!