I have a lump under my arm, but it seems to be in the muscle rather than the gland. Anyone had this problem?

First, are you a woman, I am assuming you are since you posted in Women's Health?

If so, do you have a history of breast cancer?

How long has it been there?

What is your age?

Can you remember any recent injury?

I don't know of any history in my family. I noticed it maybe a month ago and I'm sure its got slightly bigger, I went to the doctor he told me not to worry as its not in the gland. A couple of months before the same armpit was swollen and slightly tender but got better. I'm 25. Could it be fat deposits?