My 16yr old keeps getting a boil under her arm not in the armpit but below there. It is very red and sore but doesn t have a head and cant be popped. It is soft to the touch like a blister but very dark red. Pediatrician gave bactroban but its not an open sore so don t know if that will help. She has had a few of these before on the same exact spot. Last one was in August. Why does she keep getting it on the same spot over and over?