man , you are young, there are soooo many possibilities ahead. I'm 29, and I had problems with anxiety also.
in your age I got into a relationship that lasted for six years. the end of it left me with huge amount of anxiety. I worked on it , just like you, and after a while I got into the game where I wanted to find a way to really enjoy myself being with women.
it's normal that a questions regarding past comes out eventually, but what I would like to suggest is , to be mysterious about it at the beginning. Don't lie, if you don't like talking about past, it's completely ok and normal and you should stress that out in the beginning like a part of your frame she has to accept , and if you are mysterious about it, it can be your advantage regarding women. if you start opening yourself at the beginning, from my experience they might lose interest in you as a man, since they like to dig your secrets anyway, due to Electra complex, and you might get a good friend.
it's not bad but if you wanted more it can mess up your head.
the best option is to use humor to direct the conversation somewhere else.
have a few stories, true stories , prepared, and use them in those situations.But remember that it would be a good idea to be conscious of where your story can lead further conversation. have a set of stories prepared and use them due to your intentions.
for example if she asks you what college or school you went, you might say that it was the school with the most beautiful women.That can make her more interested , where you can talk about things and qualities you expect to see in women, pointing out your frame, that she will try to fit. and if you want to give her a compliment you can say that since your school you continued tradition of hanging out with beautiful women.
There is also a good thing to point out (when the talk about past emerges) that somehow you tend to remember only good or funny times, and use some true stories to create rapport , if the attraction already exist.