interesting/weird menstruation question!

Hey so I don't know a whole lot about this, but I've got a question about an interesting circumstance. So last Sunday my girlfriend and I had sex, and at some point after like 20 minutes I noticed that she had started menstruating, and I am positive she wasn't on her period when we started having sex that night. She mentioned that sometimes sex can start your period a bit early.

Anyhow, to my question. She is not on any birth control right now and I wasn't using a condom at the time. I was going to put one on but we were just thinking that since you can't get pregnant during menstruation I was okay to just finish inside of her without protection. So I did this and finished unprotected but when I saw her the next day she wasn't menstruating, and now, almost a week later, she still isn't on her period. I guess she normally wouldn't start it for another couple days, but this whole thing weirds me out a little. What is going on here? What might the chances be that she's pregnant?

 

there's a good chance

 

There's a chance she could be pregnant. It is never a good idea to bareback unless she is on birth control.

 

You can get pregnant on your period & some people can experience implantation bleeding.