How To Get Rid Of Pain In Thigh And Knee?

Hi...i'm 18 years old and last night i had a really bad throbbing in my left thigh and some of my knee. When I woke up this morning, it started to hurt again when i started walking. So i limp now, when I move. Then when I stay still it still hurts and its starting to hurt worse. I don't know what it is. What do you think?