What should i do about my lump that is in my armpit?

See your doctor: Most likely this represents an infected cyst or a small reactive lymph node but without an examination it is impossible to say. You need to make sure nothing important is happening.

Get it checked: A lump in the armpit / axilla could be a serious condition, even lymphoma. Symptoms like these deserve a full evaluation in person by your health care provider.

Probable abscess.: Probable abscess. Apply moist heat with a towel or moist heating pad and it should go away. If it gets red, bigger, you have a fever, see your doctor for antibiotics or possible i and d ie. Incision and drainage.

Axillary lymph node: Enlaged lymph node can be due to an infection in arm or hand on that side. Could be from something like monomucleosis, in which case oth nodes would be enlarged ; you would feel genaerally unwell. Possible malignancy such as breast cancer or lymphoma, is always a possibility. Localised abscess is possible, this would be tender and red ; deserves a medical visit ; antibiotics.