Several times when I was nursing, I had a pain in my breast that didn't go away and each time it turned out to be mastitis--a breast infection. It cleared up with antibiotics. Hot compresses also helped. Please go to your doctor and have it checked out.

One of my daughters also got an infected breast--she was only about 13 years old (and not nursing). In her case, it turned out she had a cyst in her breast, and she got treatment from our doctor

Weird stuff can happen in breasts! I hope you will get checked out soon.