23 year old with gradual pain

I had gradual pain in my left leg originating in my left knee. It was gradual and was thought to be the result of workouts. In April 2010 while walking at a slight incline my knee suddenly gave out and became very painful. There has been no swelling. X-rays ruled out any fractures or breaks. MRI ruled out torn meniscus. Tests were negative for rheumatoid arthritis (runs strongly in my family along with degenerative disk).  My doctor insists that I am fine and to learn to deal with the pain. However, the pain has gradually become worse, moving up into my hip and lower back. I walk with a limp and, at times, cannot put any weight upon the leg. The pain is shooting and a burning sensation from the lower back down into the hip and down the leg. My leg will twitch at times which is often followed by periods of painful jolts. I am unable to workout, limited on distances I can walk and, at times, unable to walk unassisted. I am concerned that unless I ask for specific tests or conditions to be looked at she is not going to do anything. I am in a good deal of pain and have developed stomach problems from prolonged use of pain killers and non-steroid anti-inflammatories to the point where I deal with the pain. Can someone please help point me in the right direction so I can fix whatever is wrong with me? I am only 23 years old and am terrified I may have a limp for the rest of my life at the very least.