Late Period on Birth Control

Patient: I am on Zarah birth control and am very good at taking it. One time I was maybe 6 hours late taking it, but took it as soon as I remembered. I always get my period on the Wednesday of the inactive pills. It is Wednesday right now and I have not gotten my period. Is it common to have a late period or even skip while on birth control? I have been on birth control for 11 months now, and Zarah for the last 4. I also had to take laxatives several times this month due to bad constipation, but I take my BC at night, and I never had bowel movements until the next day. Could that have affected the birth control, or would it have already been absorbed by then?

Doctor: