Kind of worried

Me and my boyfriend had unprotected sex on Saturday the 29th. He didn’t finish in me. However I took a morning after pill 2 days later so on monday the 31st. Period was fine but

Today it is April 2 and my period has drastically changed to very light to nearly any bleeding.

Could this be the plan b? Or could it be that there’s a change of pregnancy? I’m a little afraid and I know we should’ve used protection it just happened in the moment.