Which doctor should I see for a lump under my armpit?

I would definitely mention it at your treatment. Your PCP needs to know re: your over all health management. You may need a mammogram. They can also test for lupus and direct you to any specialists. If you have an online portal for any or all of your doctor's for communication let them all know.
Sending positive thoughts your way.

Hey Leanne! Given the proximity to lymph nodes, I would see your primary care doctor and mention also it to your rheumatologist. It could be entirely unrelated to your PsA. I would be afraid a specialist wouldn't consider a broad enough range of potential causes. I hope it turns out to be nothing significant and that you are just fine. Hugs! - Lori (Team Member)

Hi, Leanne!
I just wanted to check in and see how you are doing. Did the lump go away or did you get a diagnosis? I hope all is well and you are well! - Lori

Hello and Lori ( - Thank you both for following up with some advice, I really appreciate it! I have an appointment set up with my rheumy for early January. I tried to talk myself into making an appointment sooner with my GP, but like so often, life just got in the way and time got away from me. Oddly enough, the lump lasted about two weeks, went away, and another one appeared nearby a few days later. Both times, started painful, then became not too bad. I'll circle back if I happen to figure out more for others who might find themselves in a similar situation. So many doctors, so little time! -Leanne