Painful Lump in the armpit could be an abscess
in that region. Do take a course of antibiotics with anti-inflammatory drugs. Even if your swelling does not subside do undergo fine needle aspiration cytology test to ascertain the nature of swelling.You have not mentioned your sex. If female, do get your breasts examined for any lump or undergo mammography/ultrasound
of the breast.
Generally arm pit swellings are due "Hidradenitis
suppurata"that most commonly affects areas bearing apocrine sweat glands or sebaceous glands, such as the underarms, breasts, inner thighs, groin and buttocks.The simple procedure of incision and drainage
provides some relief from severe, often debilitating, pressure pain. Flare-ups may be triggered by perspiration, hormonal
changes (such as monthly cycles in women), humidity and heat, and clothing friction.
Do visit your doctor again if no respite in pain and do consider the above possibility.