What Causes Swelling Just Above Knee Cap?

I have swelling just above my knee cap no pain in the joint itself and slight swelling starting in my ankle with pins and needles feeling in my foot. My circulation seems poor in my foot, I have not injured myself and already wear special insoles in my shoes for plantafacitis. I am 50 yrs old and normally very healthy. The swelling the knee started about three weeks ago and things are not improving. What should I do?