Did she have a normal flow or was she only spotting? There is such a thing as implantation spotting that occurs in only 1/3 of girls who get pregnant. This bleeding is very light, usually only when she would wipe herself after going to the bathroom and lasts any where from one to six days. It would be light red or brownish in color.
Otherwise, it is was a normal period, she probably isn't pregnant but you won't know for sure unless you guys do a pregnancy test or find out when she gets her period next month.
If you are not ready to have a baby, my suggestion is not to have sex. I know this sounds like the normal lecture but even with condoms and birth control, it has happened. Also, she can get pregnant during her period and the "pull out" method isn't fool proof. It only takes a little sperm to make a baby that doesn't have to take a full ejaculation. If you continue to have sex (I did when I was young so again, I'm not trying to harp on you just trying to offer advice) you need to realize there is ALWAYS a chance of getting someone pregnant
yes sometimes it can mean that she is pregnant. But most likely not. If you guys are really conserned about it take a test. Its rare to have your period and be pregnant but it is possible.
One last thing I forgot to add she says that shes got stomach pain