What Causes A Small Mole In The Breast?

This is the 2nd time this has happened. I breastfeed so I pay attention to my breasts. I have a spot that I always thought was a mole that appeared while breastfeeding my 1st child but one day I pressed on it and a crusty brown thing that I thought had been a mole emerged leaving 2 tiny holes in my breast where it looked like it had burrowed. Now I am breastfeeding my 2nd child and noticed in those same tiny holes something again so I pressed & out came something again lighter in color but looked kinda crusty but not dead like the last time I discovered it. What can this be?