Me and this guy had unprotected sex three times, and all three times he pulled out and a week later I started my period is it possible I could be pregnant?

Not likely if you started your period as expected. However, keep in mind that the odds are pregnancy will occur sooner or later with the withdrawal method. If you want to lessen the chances even more, use one or two more reliable methods.

It is not likely, only because you started your period. The pull out method is pregnancy waiting to happen, there is little protection in it. There is sperm in the early fluids, so pulling out only give you less sperm, not stop it.

ANY time you have penile insertion you risk pregnancy. You can reduce the risk but not eliminate it. And the withdrawal method is the least effective way of reducing that risk.

But if you have your regular period then pregnancy is highly unlikely. But if you are trying to avoid pregnancy, you aren't going about it very effectively.