Pain in left quadracept. Strange?

I have been doing a lot of sitting lately so I am a little confused why I have a pain in my left quad. It's been there for weeks now and I limp everywhere. It only hurts when I try to walk on it or move the leg too far back or forward. Not a shooting pain or anything like that.
Sometimes it feels like it's just above the knee in the quad muscle. Other times it feels like it's high up in the quad.

It seems to be inflamed in there somehow because it's just not going away. I read somewhere that it could be from wearing my belt too tight but it seems unlikely.

Sometimes when I go to leap as if I'm going to run the pain feels like it's below the knee. Often in front of the leg but I have felt it in the rear as well.

I know it's strange but what could cause this if I haven't been doing anything very physical but walking? I'm stumped!