A keen eye might be able to feel the difference, but I doubt it. I am so sorry you carry so many things.
FM gives neuropathy type pain when the nerves get entrapped in muscles that are dysfunctional. The crazy mixed up sense of pain for us changes all pain we perceive, so it is a mixed bag.
For me, when I have a new pain, I have to think alot about it, where is it, what did I do? What could it be from and treat it as such. I don't have miltiple issues though.
RA pain needs inflammatory help, FM needs warmth and pain management as well as movement and stretch. RA needs rest and helping the inflammatory process. So they really are different roads to fix each.
I would ask that rheumy you see...."How will I know?".
I would say RA would have swelling and warmth to the area and motion issues, a sharper pain then FM. (Remember I don't have this to feel your world, I am just looking at the physiology).
Delay in RA treatment will hurt the joints more, a delay in FM treatment does nothing but the pain remains....so I would treat the worst case senario first, no change then it is FM. See if the doc agrees?
Neuropathy therapy should just continue all the time, those meds are classic and protecting your feet and hands are very important. Maintaining a better blood sugar is also part of that avenue.
I again am sorry you have more on your plate to sift through.
I have just recently been quite ill, and the doc had a hard time that I had didn't feel it coming on**, well we live in a "flu" world, so I didn't feel it coming...it was my normal creepy self, until 102* sat me on my butt! A NEW PAIN in the bones arrived and the light went on that I was in trouble!
Listen to your body closely, you may in time be able to see and feel the changes for each issue. But being attentive and alert is the only way.
Good luck, Nancy B