Aren't there activities organised at your school? You should probably join some you are interested in, to start socializing,...
Also, pay attention to people around you. Perhaps you are not the only one being excluded. If you find another person who seems also isolated, strike a conversation. The person will be more eager to talk to you than the rest of the group.
Still, it seems you should review the way you speak to people, you seem to somehow make them uncomfortable. If you just can't identify it, then speak less and listen more, in a conversation. Instead of speaking about you, ask questions about the other. People like to speak about themselves, and you will understand them better.