What Causes Recurring Hip Pain?

I am 16 years old a bit under 5"4 and I do competitive swimming and run long distance for track, I practice everyday except Sunday. I have never had any medical problems wrong with me except when I was in 6th grade I got ammonia for about a week. I have experienced hip pain for a couple months now. I can be sitting down and the pain with come to my left hip area, running or just laying down or standing. It can be livable sometimes but other times it can be unbearable and I have to stop what ever I am doing and pain medicine sometimes helps