hi i have been having a large pimple like thing exactly in the center of my nipple it also has a white head. sometimes it gets swollen and sometimes it remains small but it never goes away. up close it looks like a big zit with flluid in it. it also looks pointy. when it is swollen it feels a bit sore though. i have been having it for a long time like 2 years or so. can this be a sign of a serious issue?