Friend, I understand that the pain can be unbearable. I think your doctor should focus on controlling the pain first. Then, guide a good rheumatological study and an MRI of the knee.
You've probably already ruled out those causes. If the pain continues beyond that, your orthopedist should first consider looking at the inside of the knee with a surgical arthroscopy. If there is nothing to repair with this minimally invasive solution, unfortunately the last step for a painful knee with no apparent treatable cause will be total knee replacement with osteosesthesis.
But taking the path step by step, always trying to go from the simplest to the most complex. I wish you the best a prompt improvement. #DocChain 👨🏻⚕️