Almost sounds like an allergic reaction to something. Or, if you live somewhere with lots of deer, it might be a strange Lyme's Disease (people get this from ticks that hang around with the deer). I once had severely swollen (due to fluid) knees in March which, after a fruitless visit to the orthopedist and an MRI, turned out to be Lyme's Disease contracted the previous summer but which did not manifest till the following spring.
good luck.