What Causes Vaginal Itching Before Starting A Period?

Hi, My problem starts 3 days ago, before I got my period. This is sometimes happening before my period that I feel little bit itchiness, but now I also felt pain, something like rubbed raw from inside, only from right side when we had sex with my boyfriend. I thought it will go, maybe we were too rough, but than I got my period and still I feel little bit itchy and even after couple days wound from inside doesn/t want to grow. Can you please advise what this can be?
Thanks