I had unprotected sex with my husband 3 days before my period...?

The odds of getting pregnant at that point in your cycle are very low, especially if your cycle is pretty regular, and especially that you are getting your period.

However, the human body does funny things and nothing is 100% impossible; you could ovulate way off schedule. But that is so remote a possibility, I wouldn't lose any sleep over it unless you see a whole lot of the usual symptoms in a few weeks.

Yes. You can get pregnant at any time in the month. It's more common for an egg to release 2 weeks after your last period and 2 weeks before the next. But you could still possibly be pregnant. And even if you did conceive from that sexual intercourse, your body wouldn't respond that quickly and it would still have a period. If you miss your NEXT period, then that probably means that this is when you conceived. So to answer your question, yes it's very possible.

you are most fertile 14 days after the first day of your last period( if you have a regular 28day cylce, sperm can survive for about 3 days in your body.

If you don't want another child you should take birth control or you having your tubes tied/husband vasectomy

there is a chance that you could get pregnant right before and right after your period. but chances are slim.