What Causes Muscle Spasms In The Thigh?

Hello,

I've been having some muscle twitches or spasms in my thigh, just above my knee and a little to the left. It's been happening for several days and it doesn't stop. Sometimes it calms down some and I don't notice it, but it gets violent very often. I can't control it, and I have no idea what it is. I was wondering if anyone else knew. Thank you!