Can anyone help me?Ive recently started taking the pill but i had unprotected wiv my bf just before?

when i got the pill the doctor jus told me to start taking it that day but your meant to take it for 3 weeks then stop to allow your periods but i dont know when my period is due as i'm stil irregular and if you carry on taking the pill you dont have a period right?so i'm not gona know if i'm late so i wont know if i'm pregnant i really dont know what to do!i'm 16 and not ready for a baby!