OK, here goes. I'm 27. I was actually relatively normal as a kid, a bit shy at times when meeting new people but not any more than usual. However, when I started secondary school, I was unlucky enough to end up in a class with none of my friends from primary school, but which did have a few boys that liked nothing better than to pick on less popular people like me.
There was never any real physical abuse, but the verbal abuse was virtually non-stop for 2 years. I was pretty innocent and easy going and had no idea how to respond to it. By the time I was able to pick different classes to get away from them, my personality had changed completely. I became much more shy, much less trusting and far more socially anxious in general. I've been that way ever since. I stopped going out with my old friends after school; eventually they just didn't bother calling at my house anymore because I would always refuse to come out. Inevitably I drifted apart from them and would only see them in passing at school. Didn't make any real new friends either. My last 4 years at school weren't as bad as the first two, but by then the damage had been done and kept behaving the same way, not talking to anyone if I could avoid it.
When I started at university, I had vaguely hoped I'd meet some new friends somehow, but I had no idea how to do it and didn't really want to make the effort anyway in case it ended badly. So I basically spent the next 5 years walking into lectures, sitting on my own and walking back out again afterwards. Got to know a few people on my course a bit through some compulsory team projects, but after the projects were done I didn't make any effort to keep in contact with them. Never went to any social events, graduation parties or anything like that. Wouldn't have gone to my graduation ceremony if my parents hadn't wanted me to (I hated that day).
After I graduated I somehow managed to get a good job that I sometimes actually enjoy, but I've never felt comfortable around the other people I work with, and I quickly ended up with a reputation for being very quiet. I've been there for about 3 years now, yet I still get anxious about going out for a quick lunch with them, or going for a drink or two in the evenings, and never feel entirely at ease from the moment I walk into the building until the moment I leave. I've seen new people arrive and within a week or two they're already more part of the group than I am, and it makes me wish I could have done that when I started out.
At the moment, I've been making an effort to get a lot more exercise (mainly cycling) and eat a slightly healthier diet, to try and make me feel better about myself. I'd never actually read much about social anxiety until about a month ago, and I was surprised to see how well it described what I feel. It's also very helpful to find places like this and see I'm not actually the only person with these problems.
I've never tried any medication or therapy and I'm not convinced either one would help me much in any case. I think if I can manage to change how I think about myself, everything else will follow from that - I constantly criticise myself and worry far too much about what other people might be thinking of me, which prevents me from making any real progress.