When an young dude (or girl), arrogantly bites a nipple of another girl causing it to bleed and become infected by the bacteria surrounding the wound.
The infection can couse itching, a greenish tint surounding the wound, among other annoying simptoms. This infection should be cured before it develops a serious health hazard.
My nipple won't stop itching after I had sex.
Maybe you got a unsafe bite, you should conslut a doctor.