Just to echo what others have said, getting hormone levels etc checked out sounds like a good idea. We all lay down fat in different places and it could just be that you have a genetic tendency to put on fat there. It would certainly help to rule out other possibilities though and by the sounds of it you're quite young so identifying any hormone issues asap would be the best in the long run.

As for the other stuff, it sounds like you may be developing social anxiety / avoidant personality tendencies. Once you've ruled out the physical stuff, I'd recommend working on your self esteem and confidence through CBT or even just reading the tonnes of advice all over this website. And again, catching these things and working on them while young is all good. It took me many years to finally tackle my issues head on and I so wished I'd started sooner.

It sounds like you need to be a bit kinder to yourself and perhaps just try and spend a whole day looking for all the good things you have and taking the focus off of the perceived negatives.

Good luck, let us know how you get on.