What Causes Red And Itchy Bumps On Pubic Hair?

Hi, I have some red bumps on my pubic hair, they itch and hurt a little but it was at first just one, and I guess I itched it a bit and now there's two. My last boyfriend was unfaithful and the last time we had inteecourse was March of last year. I went and got tested with my current boyfriend in September and we were both clean. We are faithful people and do not sleep with anyone else. I'm 19. What could this be? It also started shortly before my period (3-4 days ago and I started my period the day after) and it spread a little more today. It's worrying me.