I have a knee that is giving me problems. I have been to the doctor and he said that I had arthritis in it and it would be fine although every time I do phyical activity it hurts. I was squatting and as I got up it popped and it has been bothering me ever since. It is hurting under my knee cap and there is a pain in the backside in the bend. It hurts worse to bend my knee. What could be wrong?