Milk blister/pimple??

Dafney • Married 11.3.2011 & Mommy 11.16.12 | Born & raised in New York, moved to Arizona '2015 💕 expecting baby #2 7.3.15!
Have any of you ladies had one? 
I just got one & it's really bothering me 😕 *ouch*
How do I get rid of it/treat it?