it's possible. It kind of depends on a persons cycle and when they have fertile days. Everyones different so it's best just to keep in mind that there's always a chance for pregnancy when you don't use protection.
It's unlikely you would get pregnant on your period, because most women will not ovulate on their period. But, because you did it a week later, that increases your chances. You'll need to either wait at least 2-4 weeks and take a pregnancy test with first morning urine. Like Jamie said, it is possible to get pregnant no matter when you're having sex, so always use protection and birth control if you're not wanting children.