Boils and nodule in armpit may be due to causes like simple bacterial infecion called furuncle to chronic diseases like hidradenitis suppurativa. From what you describe it probably seems to be a furucle. Kindly consult a dermatologist nearby and complete a course of antibiotics prescribed to you. If this is a recurrent problem you might need a longer therapy for eradication of infection. If its very large infection may also require pus drainage.