Hello I share your concern. Looking at your description it might be related to enlarged lymph node, axillary abscess, sebaceous cyst or local hematoma. If possible please upload me a photograph and provide more information like If you are taking any medicine? Is there any history of discharge? relevant medical history. I would advise you to take an appointment with a general surgeon or your family physician as per your convenience for physical examination and further course of action. In case of enlarged lymph node you may require further investigation like CBC, ESR, CRP, liver function test, blood sugar and FNAC if need be. At the same time your doctor should rule out possibility of metastasis by physical examination about which your doctor knows. Hope you will find my answer informative and useful, please feel free to ask for further clarification, I will gladly answer you. Best wishes