Hi OP Sorry to hear this could possibley be your diagnosis.

My sister has Lupus. And it is a VERY annoying condition to diagnose. "yes" blood tests will indicate if you have it. BUT someties that just isn't the case even if the Dr is more than certain Lupus is the cause of the pain. My sister had heaps of the certain test [geez the name escapes me atm] and only once did it come up with her levels being wrong. And that was at a time when she wasn't having a flare [go figure!].

Certain things bring on a flare for her, being run down is one of them. AF could be yours. Best thing to do is find yourself a top notch specialist.

She's had 2 more babies since her diagnosis afew years ago. She goes into 'remission' when she's pregnant, but it comes back 2x after the babes are born.

Good luck. I really hope you get the all clear and it's something that can be treated easily to help you be pain free