Why do i have a cramp on my left side and how do i get ride of it?

Im a 15 year old male and i have a pretty intense pain that feels like a cramp below my left ribcage. It hurts when i breath in deeply and also when i walk. It started hurting a few days ago after i was doing track. I thought that it was just a running cramp but it still has not gone away. If any one knows why this is like this and what i need to do to get rid of it.Maybe different stenches are something like that. Thank You.