Painful pimple in armpit. doesn't make white head like a zit. won't "pop" either. reoccurring every few weeks. i do shave my pits. what & why?

Hidradenits: Hidradenitis suppurativa (HS) is a chronic skin disease characterized by clusters of abscesses, epidermoid cysts, sebaceous cysts, pilonidal cysts that most commonly affects apocrine sweat gland bearing areas, such as the underarms. This is usually treated by excision of the infected area. See your doctor. Will persist for years if not treated.