Sorry for the double -posting.
There is one book which looks OK even to me (I'm not really that fond of self-help books). It's called "Reinventing Your Life" written by Jeffrey E. Young and Janet S. Klosko, but I haven't got first hand experience with it. It might be worth the paper it's written on.
"It's almost like a natural reaction of mine to think negatively about the people around me, possibly exerting negative body language. This negative reaction was a defense mechanism of mine. Now here I am trying to break it but don't know how! "
I believe you being consciously aware of this is the most important.
You might find it helpful to speak to a coach, counsellor or psychologist who can further help you become aware of automatic thoughts and certain patterns of behavior. It's not that easy to identify everything ourselves.
You state that it's a defence mechanism you have and I tend to agree with you in that it probably has become a personality trait. Or in other words it's actually ingrained and automatic defence responses that have become permanent(traits).
I definetely believe it's possible to identify the underlying feelings that produce certain thoughts and behaviour.
I don't have any spesific suggestions regarding tapes I'm afraid, but someone else might know of some good ones, there are a lot of tapes on how to "build" personality, also a lot of seminars, courses and the likes if one is into that.
Another suggestion is group therapy and exposure training. I believe group therapy can be one of the most effective tools in the conquering of social anxiety, but it's not for everyone.
I'm glad to hear that things have taken a turn for the better for you. You're still very young and you can definetely reverse things and learn something new(not that it's too late for anyone) You seem very determined and I wish you the best of luck with everything.