So I've Been Having Unprotected Vaginal Sex With My Girlfriend

So I've been having unprotected vaginal sex with my girlfriend for 5 months about a week ago we tried anal it was too painful for her about 2 days later she's noticed some pimple like lesions around her rectum they are extremely Painful she says it feels like chafing. We are curious about what it might be
Just to clarify we've been having unprotected vaginal sex for 5 months so we don't think it's an std