It Started With No Pain But Swelling In My Left

It started with no pain but swelling in my left ankle. Two weeks later, I woke up and my left knee was swollen as well. I have been to 3 doctors and have had an MRI. The MRI showed 2 torn ligaments in my ankle, but those seem to be from an injury several years ago and does not explain the knee swelling. All 3 doctors seemed to be stumped. When I wear braces or a walking boot it seems to make the swelling worse and there is even some pain. It always hurts more and is most swollen in the morning after being off of it all night. The swelling makes it so that I can not bend my knee without pain. This has been going on for over 2 months now.