How to get rid of a hunchback?

I'm a 17 year old male and I have a slight hunchback.I wouldnt really call it a hunchback because its not jutting out..but there is a bit of a lump. I workout for 1 hour everyday too..I dont lift weights or anything so its not because of that. Why is it there? I used to be fat earlier and now I'm thin..would that have anything to do with it? What exercises can I do to get rid of it and have a straight back.