no one here can diagnose, any medical problem over the net, not even a doctor, but I quit doing compound movements because I have the same problem, im diagnoced with tendanitus.. I have it everywhere almost now and its keeping me out of the gym 24/7. also coudl be water in the knee, more rare but easily fixed, u should be able to feel for a water pocket if thats the problem. basically for me I was advised to takin motrin 800mg every 8 hours, or 3 times per day. just to help the inflamation, try giving your legs a break and try this out for 3 or so weeks see if it helps out, also increase the h20, and consider a glucosamine supplement.
ps, 3 weeks into a deca cycle started to improve this big time for me, atleast where I could leg press again pain free.