irregular periods while on birth control?

Hi I have been on birth control for 3 months now the first two months my period started on the Saturday before the inactive pills in my birth control pack and now this month I am two days late. Before birth control I had very irregular periods and I am wondering if it is normal to have irregular periods while I am on birth control. I am kind of worried about this and have no idea about it. I have also had unprotected sex recently but he pulled out before ejaculating, I am just trying to get every possibility before considering pregnancy. Any information about this would help! Thanks!