What Causes Swelling In The Knee Joint?

I have been limping around because suddenly, I had swelling behind my joint (knee joint) in the soft tissue the round "ball" behind the knee joint. However, pain is now down in my lower leg and at times in my upper leg...all pain is in the back part of the leg. Another thing, my fingers spasam at times and I began dropping egges when making breakfeast.long before this happened in my knee joint. Also, the same pain now occurring in my left leg was happening in my right leg (same area behind knee joint, but just didn't radiate down the calf...). It was not as severe in the right leg joint and eventually went away. Almost immediately, withing a day or so of going away in right leg, it happened in my left leg. So far: I had MRIs on both knee joint areas just Saturday...not read yet. What else could this be? I'm thinking something like paulsey or something. Thanks, Denise