What Causes Red Bumps On Thighs And Butt Crack?

Hi. So I started to get this itchy feeling about a week ago, around when I started my period. Now, I've ended my period and I have little red bumps along my inner thigh close to my vagina and in my butt crack, and they're starting to flake. I've never had sex before, the most I've done is oral sex with someone else who also hasn't had sex, so we figure that rules out the possibility of it being an STD. What could it be??