What is the best otc medicine for severe chronic knee pain?

I have a shattered kneecap and have had 40% removed, a ruptured patellar tendon, a torn acl. I also got M.R.S.A. and it deteriated my prepatellar bursa so now my skin is healed directly to my tendon. I have a screw in my tibia, femur and a screw in my patella to hold my patella tendon in place. They used a 10mm graft of my hamstring tendon to replace my acl. I hurt everyday and never sleep because of it. Can someone please help?