I agree with the others. It is probably nothing to be concerned about, but any lump at any time should be reported to your Dr. All the best to you!
Ur milk ducts can extend under your arms. Mention it to ur dr and they will monitor it. I had this during pregnancy number 3. It turned out to be nothing and went away after birth.
Is in in your arm pit? I found a lump in my arm pit a little over a year ago. I had a mammogram and saw a breast cancer surgeon. He biopsied it and it came back as a benign fibroadenoma. I have it monitored about every six months, however, I was scheduled to have it checked and possibly removed last month, but I was pregnant and cancelled the appointment. Unfortunately, I had a miscarriage. But, it was really sore when I was pregnant. The hormones can make these tumors grow and be sore. Now, that my hormones are dropping and I have lost all of my pregnancy symptoms, it isn't as sore.