I am 18 years old and I had sex with my partner two days ago, and today I noticed that between my anus and vagina its red, and when I whip it hurts.
I had this before and my doctor was unsure what it was, He said it was raw and tender. I took tests and I took a papsmer and they both came back normal. I don't have any Stds. Do you have any idea what this could be and what I should do about it?

when I whip it hurts.

Well stop whipping it, that would be my suggestion.

Are you sexually active? Do you have vaginal dryness?