Pain after , what can it be?

I had last night with my boyfriend for the first time. And when i say first time I don't mean that i was a virgin, because i wasn't. Anywayz, earlier that day i had brownish discharge, and every girl knows that that means your going to be getting your period. But when we started the , no bleeding. As we went on, he said, "Are you on your period?". No, I said. Because i didn't think i was. So he kept hitting the back of my virgina, or uterus. Now today I've been having really bad stomach/uterus pain, because I'm not really sure which one it is. And i was still bleeding a little bit. He did hurt me a little bit last night by hitting my virgina/uterus. Could that be the cause of this pain? Or something more serious. Please tell me what you know/think.