I have a pimple on my left nipple with a whitehead and its swollen and it hurts ?

Blocked Mammary Duct: This def needs more infor and a work-up just because of the location and little info we have on you in this forum. However, the most likely finding of what you describe is a blocked mammary duct; essentially a clog milk duct that may or may not be infected. These are gen easily tx'd. You likely have very little reason for concern; however not knowing a lot more I have to rec further evaluation.