Thanks for writing here.
It seems you have ingrown hairs in your armpit.
These are curved hairs and irritate the skin.
This will lead to skin damage and infection with bacteria.
Apply a topical antibiotic
cream like t bact over bumps.
Avoid any deodrants.
Use good toilet soap for cleaning area.
Ingrown hairs can be treated by lasers .
You need to consult a dermatologist
Hope this will help you.Take care.