I Had This Pimple On My Nipple For About Two

I had this pimple on my nipple for about two months now. Some days it would hurt some days it wouldn't. So last night I decided to squeeze it because it looked like a "white head" and a little puss came out. Tonight I spqeezes it again and this hard white stuff came out. It looked like a sesame seed. Now I have a hole on my nipple and hurt when my clothing rubs against it. What should I do?