Re: left breast/armpit pain -if it's not cancer, what could it be ?
It could be:
Mastitis - inflammation
Hormones - see if it gets worse/better through your cycle
Cyst - filling and emptying
Infection in armpit - may or may not cause swollen lymph nodes
Infected sweat gland.
Hope you get to the bottom of it. See a doctor and find out what it is. Sera