"Lupus" would be my answer - I could truthfully answer any of 5-6 diagnoses that have shown up on my chart from time to time, but for simplicity sake, and consistency as well, that's the one I've pulled out of the bag and used for over 10 years.
You could also say "I'm being treated for Lupus and RA". Or you could say "overlapping auto-immune disorders", that would cover it all. I'm having a Lupus flare....it's not like most of these places/people/situations know much about
these diseases anyway.
I don't know where you are located, but if it's in the US, there has to be a diagnosis, or suspected diagnosis, that shows up in the medical paperwork. Maybe you could ask for a copy of your medical records and see what's written in there.
Just take a big breath and let yourself be a bit ambiguous and mysterious!
Lynnwood, Lupus & Sjogren's Moderator, Dx: 2002DIAGNOSING LUPUS & LUPUS RESOURCES
"Life is far too important to be taken seriously." - Oscar Wilde