It is unlikely that missing a pill would affect the effectiveness of your contraception. However, it is important to continue taking your pill even if you have your period. Factors such as stress and hormones can influence the onset of your period, so if you have experienced two cycles in a row where your period is "out of control", it would be best to contact your gynecologist or doctor for advice. They may be able to change your pill without needing to meet with you, depending on your medical history.