Re: can you get pregnant on the first day of your period ?
I agree with Kszan completely, based on your account about the whole thing.
During menstruation, your body is sloughing off the lining of your uterus, which has not been used for implantation by a fertilized egg. That would have been you last months period, not even this one. You are not pregnant. I do understand your concerns though, and good for you to be on birth control and being so careful. I would go one step further though, and have him use a condom as well. Condoms make STD's less likely, as well as protect you from pregnancy. Good luck!