My confidence improved at university, I was really bad at school but got gradually better at college. You just need to psyche yourself up, and take everything gradually. Small talk is the best way to start, really, find out little bits about people or whatever. It's easier in group situations since you don't have to say so much, just contribute every now and then and try and relax.
University will give you a shock at first but you just need to adjust to the environment as soon as possible. Think of it in these terms, everyone is in the same boat as you, most there have probably only just moved away from home also and deep down, although they may not show it, are scared and nervous and all that. You can relate to people instantly because of that, and everyone wants to make friends at the start. Take it gradually, and don't do anything you are uncomfortable with. It sounds hard but you'll feel great once your confidence is higher.
Oh, and about comments or whatever about how you look... try not to be self-conscious. Everyone looks different, ignore comments from other people. What right do they have to say anything about you? None. Be comfortable with who you are and confidence will come from there.
I may be a little bit of a hypocrite saying all of this, but a lot of it is drawn from personal experience (if not all of it). Good luck!