Mysterious aliment – what's wrong?

For quite a number of months I have had swelling and soreness in various areas of my leg from the knee to the ankle/foot. An area such as an outside tendon will get somewhat inflamed and quite sore and stiff for a week or so. Then it will dissipate and show up under the kneecap or some other part of the knee. There is always some place that is affected. Two weeks ago the knee seemed better than it had been in months and then my ankle and lower Achilles tendon swelled up and was quite sore for a week. That disappeared and immediately there appeared a swelling above the knee and accompanying stiffness and soreness. At times it is quite debilitating and I am either limping around or even using a cane. I’ve been to 3 drs and 2 nurse practitioners, x rayed, but no one can seem to put their finger on the cause of this. Anyone ever hear of this kind of thing?