Hi and welcome to the forum! I am glad that I can help you.
You want to know what a lump a size of a pea under your armpit is.
There are three possible diagnoses for a lump the size of a pea under the armpit: enlarged lymph node, folliculitis or hydradenitis. Enlarged lymph nodes may appear in local or general infections or in metastatic dissemination of tumors. Folliculitis is an infection of the hair follicle and is treated with antibiotics. Hydradenitis is inflammation or infection of the sweat glands. If both folliculitis and hydradenitis don't heal after taking antibiotics, a small incision is required to drain the pus.
Given the data that you described, you may experience one of the conditions listed above. You may consider seeing your doctor for further diagnosis.
Please keep in mind that I provide medical information only. I am not able to diagnose medical conditions online. Please contact your doctor for further advice and information about diagnosis and treatment options.
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