Puss filled bumps under large breasts? I have very painful bumps under my breasts, what could they be?

Infection. Pus is a sign of an infection and should be evaluated and treated by your doctor. Don't hesitate as infections can spread an worsen.
Infection. Could be an infection with bacteria, fungus, or yeast. You need to see a doctor and have the lesions cultured to identify the infectious organism and get proper treatment. It can get worse and spread.
Candida. Candida is a common infection in fold areas such as under the breast, in the groin, amd in the armpit. This is more common in women with large breasts and in women who are diabetic. Until you see your doctor to rule out diabetes, open wet compress with water to dry out blisters with dilute vinegar solution followed by mica tin cream twice a day. Then zeasorb af powder.