First of all, I sincerely apologize for the delay in getting a response to this. You definitely should not have had to wait this long for an answer. Hopefully this response will still be helpful to you. It's good to hear that you have already sought treatment for social anxiety disorder. That is a very important step towards eventually overcoming the disorder. However, it sounds like you might need to tweak your treatment plan a bit. People with social anxiety disorder can absolutely live very normal and symptom free lives, but like any other psychiatric condition, the medication dosages and therapy must be correct.
The fact that you are still experiencing such strong symptoms indicates that you haven't quite found the perfect treatment yet. This is something that you should be able to work out with your doctor. Perhaps a different dose or slightly different form of anxiety medication would take care of the problem. The introduction (or increase in, if you already are) of one-on-one therapy with a trained professional could also help solve this problem. Sometimes it is really helpful to be able to talk to someone who can help you sort out these irrational thoughts and get you back on track.
You may also want to try a few other things to help out with your thinking. When you start having these thoughts, instead of freaking out right away, try concentrating them elsewhere. Get out a journal and write down exactly what you are feeling and why. Then read through it again and try to make sense of it. If you don't like writing, try drawing or some other form of art. Even going out on a run or painting your nails....anything to get your mind off of the obsessive thinking can help. It gives you a chance to blow off some steam and rationalize what you are fearing.
What it comes down to is that the thoughts probably will not just go away on their own. One of two things needs to happen. Either you need to adjust your medication, which will physically even out any chemical imbalances that are causing these thoughts; or you need to change the way you deal with them. Try new things until you find something that works for you-don't give up. It might seem like you have been dealing with this problem for forever, but you are still young. There is definitely hope that one day these unwanted feelings will go away, and you can lead a very happy life.
I really wish you the best of luck with all of this. I know you can do it.
If you are ever feeling really anxious or need someone to talk to about how you're feeling, or just need to rant, PM me. I'd be happy to help you out any time.
A resource you might find useful...
Anxiety tips
http://www.a2zpsychology.com/ARTICLES/TIPS_ANXIETY.HTM