Im having some chest pains?

I'm a 16 year old girl and last year i started to have some chest pains. Sometimes when i would breathe in it would hurt right in the middle and id have to stop for a little bit but it would go away quickly. I went to my doctor and he thought it might be bronchitis so he tested me and it wasn't. He didnt do any other tests and after a while it didn't hurt. A few months ago it started again but only once in a while so i didnt say anything. For the past week its been more recent. My mom wants me to go to the doctor again but i dont reallt think its neccessary. Any ideas what might me causing that??