What is the root cause of social anxiety?

[LadyGamer]

Hello, I'm a 21 year old female, and I get frequent anxiety attacks when I'm in public places. I notice that I get them when I'm in a super market, the mall, restaurants, or anywhere that is overly crowded. When I do get them, my chest begins to tighten, and I feel that the people around me are judging me. The questions that around flying in my head are: ' why are these people looking at me?' 'what do they think about me?'. I'm a college student, and I use to be able to give oral presentations as if it was nothing, and now its difficult and painful emotionally. I dropped an English class because I wasn't able to concentrate and the class was based on speech techniques. Now I'm worried if I will be able to graduate with my degree in performing arts, or just filed for a new major. I really love music and hope to become a music instructor but this social anxiety is killing me. What do I do? I don't wish to be taking any medication because last year, I was treated for my depression/anxiety with Prozac, and the drug was doing damage to my stomach. Any recommendations?