I'm 60,female, healthy. Foe exercise I do walking, yoga and Falkland bicycling. Have never had a knee problem in the past. Developed significant swelling on top above my right knee, soreness and some pain on the outside of the knee, along with some stiffness and less ability to bend it without pain. Using 2/200 mg ibuprofen am and Aleve 200 pm, and ice on it. What can be causing it?