Leeness I know exactly how it feels, and I'm similar in many regards (despite being a guy).
I have a very low opinion myself (looks and abilities), and I'm generally not sure if I'm overly critical, or if I'm just not good enough. I too was called nasty things during my teenage years, and like with you they still haunt me to this day. Having said that I am starting to think higher of myself nowadays, and despite my issues it has seemed to help a bit.
A lot of my issues over the past couple of years have come from my uncertainty in the future, my regrets, my lack of outgoing friends and my career choice. All of which are intensified due to my OCD, which isn't exactly helping the situation.
I'm personally trying to get to where I was with confidence back in 2010 (second year of college), and then go beyond that state. I was highly regarded in skill by my tutors/classmates, I had hopeful ambitions for the future, and I was just generally happier with myself. I guess all of this caused one of my friends (who I had a crush on in my first year) to fall for me, and we dated for a bit, but I (somewhat regrettably) ended it (as detailed from
here in the first dating thread). It did give me a huge confidence boost though, and I even seemed to overcome a few hurdles with my approach anxiety (I was still unable to approach people directly, but I did seem to open up to strangers better). Sadly however for a variety of reasons my confidence vanished in my final year.
These past couple of weeks I've been telling myself something positive and unique about me, and you know what? It has helped a bit, so I suggest trying it!

I've also been listening to some
confidence building music (as suggested by Cubsfan23) and they're great! I'm not usually one for that kind of thing, but they do seem to help a bit, somehow. Also I'm not saying you have to drink, but what have you actually tried before? A tiny bit may help loosen you up a bit, and thus make you more approachable. The thing I find with alcohol is that it can be enjoyable, but you just need to know what you like drinks-wise. Even just going out in the evening to bars with friends would be good, even if you don't drink.
Anyway I'm sorry I haven't helped much, and I hope things work out for you soon!
