Go and see a doctor. I have two questions for you, the answers to which can change your course of management. 1. Do you shave/wax your arm pits? if yes, it s very likely that you have folliculitis ie inflammation/ infection of hair follicles. If you use topical antibiotic while they are still tiny, you can, most of the time prevent it from developing into an abcess. Once, they grow in size and pus collects within them, they have to be drained. 2. Do you have cats? Have you been scratched by a cat? This could present with similar symptoms for which you would need antibiotics besides drainage. Either ways, see your doctor.