Knee pain: under and below the knee cap-when I stretch it there is sharp pain. I've been icing it, but doesn't help. Hurting for more than a week.

Varies. There are several possibilities including tendinitis of the patellar tendon at its orgin on the patella or chondromalacia on the under surface of the patella. You would probably do well to avoid jumping activities and activities that involve a lot of knee flexion, and if it does not get better I would consider being seen.