I am having severe knee pain. Knee cap area more on inner leftside side and down slightly, Very sensitive to touch, slightly swollen, concentrated in an area a little smaller than the size of a tennis ball. It ached, throbs, hard to walk, bend, sleep. I tried ice, aspirin, ibumotrin I am miserable. I do not remember injury, it came on over a week or so, rest helps a little and if I walk stiff legged it does not hurt as strongly. What is this, what causes this, what should I do