I know exactly what you mean. Although this isn't entirely the same, at my old highschool I thought people believed I was gay, or homosexual, whichever is least offensive to you. For starters im not, but I would always pick up on small things people said and warp it into the big ol thought "THAT GUY IS GAY". Even though I have done things to back up the fact that im not.. I couldn't get over the thoughts and I always felt like people were reading into me. That was at the peak of my social anxiety though, and although my SA is still bad, I have learned to cope a bit. I haven't smoke weed for about a year now, and I think that is what helped me most, because weed always makes me think more than I should. Am I breathing heavily? Am I doing something weird? Oh that girl is looking at me funny, am I wearing something weird? Am I ugly? Oh man I suck..
Thats what it was like for me when I was high. And the worst thing is, I kept doing it for a while after these intense episodes for some stupid reason, which I think made it stick around even after quitting. It essentially changed my person. But now everytime I have thoughts like those, excuse my language, but I say "who the **** cares what this guy thinks about me?" although I still can't make friends very well at all, and I couldn't do things with a large audience to save my life, it has helped me at least go out more.. I think in time with more practice and age, I will grow out of it. Which is the only reason I give effort, knowing and hoping one day it will not control me like it does now.