i have rheumatoid arthritis, so does everyone else in my family. i'm lucky, no symptoms till my mid thirties, rapid decline now. but my sister had JRA since she was 2 and has already had major reconstructive surgery on her knee.
try not to stress too much. whatever it is, it is what it is. you've probably had it forever and probably so have family members.
everyone has something, some bad deal in their hand. it's just another thing, one day at a time, enjoy the good days, rest up and do what makes you feel good on the bad ones.
personally, i had a much harded struggle with the mental stuff before i gave up struggling and decided to just take what comes and be happy i'm still here.
i don't get too hung up on diagnoses, either. naming my demons just makes them stronger in my mind.
and this may either be comforting to you or make you really mad, but personally, i feel like we're all alive to learn something, and that without barriers and problems, we would learn nothing. so i really do feel that suffering can teach us a lot - sympathy, empathy, patience, charity, just to be more like god, whatever your concept of god may be. i think these kinds of problems help us to understand other people and to be more thoughtful.
or maybe it's just a crappy deal and we just have to deal with it.
i like the god thing better tho - if you're going to suffer, there may as well be a point.
good luck to you, whatever happens.