I am 20 years old and for the last few years I can only stand for about 5 minutes before my back starts to hurt and I start leaning over. Also, after about 20 minutes of walking my knees are in severe pain and begin to swell. If I walk longer than that it gets to the point where my back is hurting, and my legs are throbbing. When I go to sit down to eleviate pressure from knees it is hard to straighten them out it hurts so bad. A few years ago I had acl reconstructive surgery and wonder if all this is due to that? The other day I went to the doctor for something else and decided to ask her since I was there. I told her about the back pain, and she told me I was fine and I didn't get to finish telling her anything. I feel stupid now for asking about it again, but there are times when I am in so much pain I just lay on the floor. I know people's joints will hurt after walking for awhile, but is it this severe? Should I see a doctor or will he just think I am being stupid?