Nervous around new people or groups of people?

I am not very comfortable with myself, and I never have been. I know that I'm not necessarily pretty, but I'm not ugly. I can be comfortable and myself around my friends, after knowing them for a while. But when I am around new people my heart starts beating faster, I get really nervous, my eyes start to water and it gets harder to breathe. I get really nervous with everyone watching me, and I don't know why. I think maybe its because I don't know what they are thinking when they look at me. I dont want them to think I'm ugly or weird, and for some reason it feels like I'm going to explode from the pressure. As soon as everyone's looking at me I want to run away as fast as I can. In class, I avoid being called on at all costs because it means everyone looking at me. I don't get it, why can I be so outgoing and fun around my friends, but as soon as I'm around new people I like automatically stop talking because Im scared that ill say something they wont agree with, and they wont like me. I dont want to be like this!! What is wrong with me?