I keep getting pimple like bumps in my armpit. i had one recently drained but 3 weeks later i've 3 small ones. they are quite painful and come and go?

Could be: something else. With a description like that I would be concerned about hidradenitis. It is a condition where the sweat glands become infected and cause repeated infections and abscesses in the areas of apocrine sweat glands (underarms, groin, under the breasts). You should see your primary care doc. Antibiotics and conservative therapy first, but surgery is sometimes necessary.