<s>[INST] Hello, I was just curious. I m 20 years old and have a lump under my armpit it s been there since I can remember and my doctor years ago said it was nothing to worry about just fatty tissue. However I ve noticed it gets sensitive during my menstrual cycle, what could this be? [/INST] HiWelcome.I have gone through your query.It is difficult to comment on it without examination, so I would either suggest you to see doctor for examination and for exact diagnosis or upload the pictures here, I'll go through them, and provide you with specific advice.it might be folliculitis or lipoma, need to be examined to confirm.Hope this helps.Take care </s>