I get underarm pain as well as rash. I use a scrub in the shower or an amazing loufa....natural one or a sisal bursh just to exfoliate so no ingrown hairs to cause bumps as the pain is bad enough. I get them occasionally. I have used a scrub made of sea salts(large grain) baking soda, epsom salts and any essential oil I felt needed to be added.

Massage therapist can help to remove lymp flow in the armpit and get the lymph area moving again. I had over 80% occlusion of subclavian vein before I had my surgery so was really swollen at times.

Heat and bad deoderant doesn't help a rash either. I hope you can get things moving again,
Best of luck,
Victoria