What Causes Knee Swelling And Pain Post Reconstruction?

HI i m David and i m in the military station in Japan. I had 3 surgeries over the past year and half. The last surgery was late February 2011. When I went under a second surgery for a reconstruction of my right AC joint dislocation, the doctors in Hawaii use one of my ligament from my right knee connecting to my leg to perform the surgery. Is been 8 month s or more since the surgery and i m starting to have problems with my knee. My knee right now is swollen and it get s stiff at times as if it want s lock itself. Also it hurts when going up the stairs and pushing my weight up with my right leg to go up the stairs. I should mention that before any of this pain started to happen to me i was running a lot playing soccer everyday over the this summer. Can any doctor help me answer what seems to be my problem with my knee and why is it swollen. the pain at times on a scale 1-10 goes up to 8 in pain.