What Causes Swelling In The Knees?

Okay so last Friday in dance class we had to jump as high as we can without bending our knees. The next morning I woke up and my legs were hurting. Now it worse and I have a bit of trouble walking. I not sure what's wrong with my leg. also it not swollen. I don't know what to do I really worried its injured plz tell me whats wrong with my leg