I think you're internalizing too much stuff, too much, in social situations. I have trouble with that too.
Also, all of this stuff you feel inside, everyone else feels that way at some time or another, but since it's on the inside, people don't see it and you look "normal" to others. I remember a sociology professor talking about how everyone has a "stage" and a "backstage" in our lives and, by nature, we tend to compare our "backstage" to everyone else's "stage". Thus leading to feelings of inferiority.