Could I be pregnant?

So I decided to stop taking my birth control for health reasons, I took my last pill Friday, August 10th. I still had 4 pills left in my pack (21 day pack) that I did not take. I started bleeding Monday, August 13th. My fiancé and I had unprotected sex without pulling out Tuesday, August 14th. I’m not sure if it was an actual period or just a withdrawal bleed from stopping the pill. Could I be pregnant? When would I be able to test? My cycle is going to be out of whack so I do not know if I should base my expected period for September off the day I started bleeding this month?