knee pain

Our user asked: "I'm a 20 year old male, slightly overweight(football player). Around 2 1/2 years ago I injured my right knee playing high school football first by landing on it directly and then by twisting it. The pain that resulted was a dull pain every time I climbed several long flights of stairs, heavily exercised, or had to keep my knee in the same position for a long period of time(e.g. going to a movie, or a long car ride). Eventually I went to physical therapy and my PT told me it was probably tendinitis. After a few months of PT the pain went away. Fast forwarding to now, about two years after the initial pain has gone away I started an exercise program that includes 45 minutes to an hour of daily recumbent bicycle cardio. All was well for the first few weeks but one day this week I got this pain on the inside or left side of my right knee after exercising. The pain started out pretty light and just occurred when I had to use stairs and support all my weight on one knee, but now about a week later (and continued exercise)there is almost constant pain in my knee. Every time I extend it or move it I get sharp pains. My knee is pretty tight right now but there isn't any swelling I can see. Also, the pain seems to run along side the left edge of my knee cap if that is relevant. Any ideas?"