My boyfriend has Behcet's disease and RA and as soon as they started him on immunosuppressents/prednisone he began getting large boils on his shoulders and back. For him they are one of the minor side effects, but he totally understands what you're going thru. I'd suggest getting a referral from your rheumy to a dermatologist. There are a lot of different things they can do to address that issue. If left untreated they can scar.
Hope this helps :)
DX- SLE, Arthritis, DDD Lumbar, Hypertension, Hypothyroidism, Diabetes, and MDD
Medicines - Methotrexate, Folic Acid, Hydrocodeine, Etodolac, Ibuprofen, Acetaminophen, tizanidine, Norvasc, Levothyroxine, Metformin, Glipizide, and Viibryd