Did I get my period because I stopped my birth control?

Yes. Your body does not have a calendar, so it does not know when you stop your pill in the middle of a pack or when you get to the inactive week. So if it sees the hormone levels drop, it will bleed.

It is unlikely that you will be pregnant, but not impossible. You can take a pregnancy test 21 days after the sex. Repeat it 7 days later to confirm the results.

If I had sex like that again, right after my period stops, what do you think the chances will be of me getting pregnant?

It is not possible for me to say. Some women will get fertile immediately, some will take a month or two.

At the very best, having sex on just the right days and not being on the pill at all, the chances are only 30% that you will be pregnant.

Best of luck TTC!