Hi heatmiser, It's very common to have overlapping disease. You do have something going on. If you don't have them get a record of the labs you have had done. a Possitive ANA is one of mean sign. but the rash also. I have leg problems as well but after 6 months on plaquenil they started to improve.
I would find a rheumy that no about auto immune disease. Some are only trained for arthritis. take pic. of your rash because they won't be there probably when you see the doctor. I'm sure with your other health issues you know the drill when talking to doctors. Lupies tend to run fevers so you might try to take your temp twice a day and document it. for the doctor. usually under 100.00degrees
You asked about weather it was better to find out sooner or later. I would say if you can find somthing that will help you enjoy a better quality of life you should jump at the chance.
Good luck and let us know what you find out.
Love people and use things, not love things and use people............