It depends (sorry!). It won't be due to the pills, I think I can say that much. If you bleed, then you would probably have bled if you were off pills as well. The only way to know is to test!

Yes it's possible, but very unlikely, and even more unlikely if you have been taking your pills correctly.

If you get your period while on the pill, it's very unlikely that you're pregnant, because you're still shedding uterine lining (which the egg usually embeds in) even if there's no egg to be dispelled. Get what I mean?