Irregular period after Birth control

Hey ladies, I've have been puzzled for a couple of days about my "late" period. I was on birth control for a couple of months got off of it and I had my first normal period since a long time. I had a regular ovulation and I was waiting for my period to start but it's 15 days late now. A couple of days after my ovulation I took a pregnancy test and it was negative. So I'm wondering why my period is late..? Could it be because of the birth control?? I have an appointment with my doctor but it's not for another 2 weeks I'm just wondering if this has happened to anyone before