How long is your right armpit very sore?
Do you have any other symptoms such as itching, redness etc.?
How big is the lump do you think?
Did you shave your rigt arm pit recently?
Do you use anything for under arm such as deodorant , antiperspiration spray , lotion etc. ?
Did you try anything so far to take care of this problem ?
How is your general health ?
Please answer the above question for a better evaluation of your condition.
Since the armpit is very sore i suspect first of all an abcess under the armpit skin. Other possibilities that needs to be ruled out an inflamed sebaceous cyst or infected or inflamed lymphnode in the armpit. The etiologic agent causing this lump and pain could be a bacteria, a virus, a fungus or a tumor. The chance of a tumor causing this is less since your right armpit is very sore. Swollen lymphnodes due to a tumor is usually painless. You need to be treated according to the cause of this problem. To find th cause you need a physical exam and appropriate tests following the physical examination. I suggest to you to see a doctor. Please click the link below for more information:
I hope this helps. Please you let me know if you need more input.
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