If it's still bothering you, you may want to talk to a dermatologist about it. It's most likely folliculitis, which is caused by clogged hair follicles. It's possible that it got irritated or infected. For now, it's best to make sure to wear clean clothes ( most importantly, underwear) and not to use irritating soaps or anything. Also, when you get out of the shower or swimming pool, make sure to dry off thoroughly and keep dry/clean.
A dermatologist can help you out more, maybe even by prescribing a cream.