What Causes Sharp Pain In The Chest?

I am a 20 year old woman in college and I jog, play soccer, and do college level gymnastics. Four months ago I started experiencing sharp chest pains sometimes 10 times a day that last normally a few seconds. They can be various places in the chest. I have had complete bloodwork done to check for a hormone imbalance, a chest x-ray, and I also had a Echogram done. All are normal. Any suggestions?