Why did i bleed after sex?

Okay so I just had sex last night he was rougher then usual . It kinda hurt a little like a stinging pain but i ignored it . When i came home i went pee and a looked in the toilet and there was a drop of blood i wiped and there was no blood on the toilet paper . im scared . could there be something wrong ? im not bleeding no more but i still have a little of that stinging pain . and this weird not really pain full cramp in the middle of my tummy .