Hi Finoa - This could be an enlarged lymph node or (much less likely), a sign of cancer. Since you've already had it 3 weeks and it doesn't seem to be going away, it's probably time to see a doctor. In the meantime, please read our post on armpit lumps, for lots of good information about what might be causing this. Good luck - PJH
It could just be a blocked sweat gland Fiona. Consider stopping the use of antipespirants for now. Antipespirants can clog the lymph nodes in that area. If the lump is very hard and feels like a pebble it is more likely to be something serious. Otherwise it is probably something normal. But whatever it is, see a doctor. Try to stay calm Fiona, most likely it is nothing at all.
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