Dance injury.. What is it?!? OW!?

Okay, the other day I was extensively dancing (I had 5 classes that day). Usually when I come back from dance I'll have this pain on the muscle right inbetween my kneecap and above my shin bone. It's a really sharp pain and whenever I put pressure on it such as walking, that muscle right under my knee hurts so bad! So that other day I came back and was like, 'Oh, it hurts. Better ice it.' It usually goes away after about two days, but this still hurts after seven. Can you tell me what's wrong with my knee?!? It hurts :( All I can do is ice it. Please help.