If you aren't taking birth control the way it is supposed to be taken it can effect your cycles. If you got a period then most likely you're not pregnant.
Do you wanna be preggo? Because if your on birth control yes you can become preggo but not likely depending on what bc your taking, but most likely your period was just a little off balance due to your bc, but at the same time you could be preggo so just take a test and then you'll know
Best wishes