I get nervous around people. Like hell.

I don't know what to call it when I am around people suddenly my mood changes and I feel not myself . I have been introvert in my childhood but once I become on my own alone and do everything myself ; I get nervous/mood-changing around people even around my family sometimes. At that time I just want to be on my own which I don't like it . I fight with nervousness and it makes it worse. Even my closest friends tell me that I am not myself most of the times around them . It just bothers me so much . I don't want to get nervous or anything. I am an active student at my college but when it comes to being / dealing with people (even my close friends) , I get nervous and make them feel alienated around me . It bothers me like hell.