Rheumatoid Arthritis Support Group
Rheumatoid arthritis is a chronic, inflammatory, multisystem, autoimmune disorder. It is a disabling and painful condition which can lead to substantial loss of mobility due to pain and joint destruction. The disease is also systemic in that it often also affects many extra-articular tissues throughout the body including the skin, blood vessels, heart, lungs, and...

Is it in/at a joint? Which one? Closest to the finger nail [call that joint #1]. Or further towards the wrist? I'm wondering if it's a nodule. Check out this site and look at picture and see if it resembles what you have.
https://www.google.com/search?q=image+rheumatoid+nodules&rlz=1C1PRFC_enUS713US713&espv=2&biw=1067&bih=473&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjJ1vDhnvnQAhVP_mMKHXc1DZEQ_AUIBygC&dpr=1.5#imgrc=hpLVao59Qu-eaM%3A
When's your next rheumatologist appointment? That's the best place to get a diagnosis.
Do you have an orthopedic surgeon? I'm thinking it's something they gan aspirate in the office [if it's capable of being aspirated....i.e., it's not solidified]. But if so, I'd have an orth surgeon who does hands do this.
Sorry, not much help, but this is a crazy disease.....
Another thing is that you can get big osteo growths on your finger joints, especially the top joint. That happens after the joints have been damaged. I do wonder, why I never had them in 17 years, and they just popped up after a major med failure? In other words, it was a bit too much coincidence for me to believe it was just OA appearing in large deforming amounts in the PIPs. (Top finger joints!)