Why does the Top Side of my Thigh Hurt?

So on Tuesday I was at my dance classes, and my legs felt a little funny, but they didn't hurt

I woke up yesterday, and the top side of my thigh is intensely hurting. I'm limping, and I'm going up stairs very slowly, and pretty much hopping step to step going down. It basically hurts to lift the leg

Then yesterday I had a television performance for a local channel, and I had to do my dances pretty full out for those. Then tonight I have to go to a ballet class, and I can't skip it because we're working on recital stuff.

So. My question to anyone who may know, what could be wrong with my leg? About how long should it take to heal? Should I stretch? Also, would it make it worse if I even just go easy at ballet tonight?

Thanks :)