I had sexual intercourse with my boyfriend last night. And after I noticed blood.. Not a whole lot but enough to notice.. When I went pee there was blood in the toilet and on the toilet paper when I wiped. It couldn't have been my period bacause I had just finished my period about two weeks ago. This morning I showered and I wasn't bleeding. We ended up having sex again and we had to stop bacause he noticed bleeding, once again it's not a whole amount of blood but enough. I lost my virginity a year ago and me and my boyfriend had taken a brake from sex for a month or so.. Why could this be happening?

Some additional tearing, rough sex causing the bleeding.

Could be any number of reasons. He could have been too rough, you may not have been lubricated enough, maybe you weren't relaxed.

The vagina is very sensitive. It doesn't take much to cause damage.

As the above posters say, rough sex and/or you may have not been lubricated enough! Always make sure you're wet enough.
But DON'T worry girl, just don't do sex for some time so it gets to heal itself first ;)
After that you'll be ight! Have fun and always protect yourself!