Okay all medical personnel out there I need some quick advice...

Recently, I started to experience a soreness in one of the muscles around my knee. Sometimes it's a simple pain (nothing crippling) and sometimes it's a burning sensation. I'm not exactly sure which muscle it is but it's on the back of my left knee right next to that tendon/ligament that holds the kneecap in place.

Any ideas, thoughts or suggestions? I don't think it's a rip or a tear. I really would just like to hear that it's sore from being worked...