For the last two months I have had a hard, painful not in my left underarm and was prescribed penicillan because of nursing my 6 mo. old. Both times it went away.  This month it has occured again but in the other arm and I am begining to become concerned.  I am an astmatic with bad allergies and have a hypothyroid.
Welcome to Chat Doctor .1. They are infective cause with collection of pus within - most possible cause could be hair follicular infection.2. Which needs an antibiotic treatment, in case of larger and recurrent ones - it needs a small incision and Chat Doctor. 3. But once for all remember - do not press or scratch the lesions / lumps, you will only make it complicate it.4. Avoid cloths which cause friction / irritation that will also cause recurrence - use sod nature of the clothing.5. Maintain local hygiene, keep area clean with antiseptic liquids, avoid shaving until completely healed - meanwhile use trimming instead.6. If you follow above it will gel in complete cure. Good luck. Hope it helps you. Wish you a good health. Anything to ask ? Do not hesitate. Thank you.