could have a cyst or a ingrown hair go get it checked out
Welcome to the MedHelp forum!
Since you have pain in the armpit, it can be due to heat intolerance and due to sweat dermatitis. It is also possible due to peripheral artery disease. Peripheral neuropathies as in diabetes, chemical burns due to any deo or lotions you use, peripheral nerve compression are the other possibilities.
If there is a swelling, then it can be a swollen lymphnode, in response to fungal infection or sweat dermatitis or infection of hair follicles. It can also be folliculitis or a hair follicle infection. It can also be an enlarged lymphnode due to malignancy of breast (rare in males but not impossible). At times it is a cyst too and this can get infected. Consult your PCP for an evaluation. A CT scan can be confirmatory or a fine needle biopsy. Treatment can vary from wait and watch to anti-inflammatory along with antibiotics to excision of the lump.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!
Lymph nodes are under your arm. They can swell and cause pain. If you feel any lumps or swelling and this persists you should contact your doctor. Pain could also come from a pulled muscle, you could try Ibuprofen and see if that makes it better. Good Luck.