What Causes A Painful Labia Cut Like A Stretch Mark After Intercourse?

I have a cut,im not sure how to explain it,it looks like a stretchmark ripped open,but i guess thats imposssible,its on my libia, it happened after i had sex,i was in the shower when i discovered it,it hurt like a cut,but it doesnt anymore,it might of been from rough sex but i just dont know its not bumpy or itchy or painful its just there,like sorta a rash.