Have I pulled a ligament in my knee?

I think I've either pulled or strained a ligament in my knee. I think it's the "medial collateral ligament". My knee would hurt if I crossed my legs and after a long period of time it would really hurt such as it would hurt to let my leg go straight of if i bent it and sometime I can feel as if it's pulling if I walk. I'm not really sure if I have but, I play football and run a lot so I want to know if you think I have before I got to the doctors and that. I'm just really worried:S