What could this chest/breast pain be? HELP?

For a few weeks, maybe months, I have been getting bad chest/breast pain. I'm 15, so very young, My mom tells me it's just "growing pains" but every time I've "grown" before, I have never felt any pain, ESPECIALLY not like this. Normally, it comes very random and sudden, I can't move or breathe, It feels like someone is stabbing me repeatedly in the chest. At first I thought it could be heart attack, but then maybe Breast cancer? There are no lumps, but it could still be breast cancer... recently, like last night and today, the pain won't go away. I thought it was heart attack, because it was only on the left side. As of last night, it has moved to the right side, same place. I mentioned it to my mom again last night, and since I went to bed, it still hasn't gone away. I cried myself to sleep in the feeble position last night, it's getting so bad! Please help?