This study is a pilot, randomized, placebo-controlled trial evaluating the treatment of Premenstrual Dysphoric Disorder comorbid with Bipolar Disorder using combined oral contraceptives. Lay Summary: This study is being done with the hope of finding a safe and effective treatment for individuals who experience both bipolar disorder and severe premenstrual symptoms. As part of this clinical trial, participants will receive either a combined oral contraceptive (i.e. oral birth control pills) as a treatment for severe premenstrual symptoms or a placebo (a pill without any active components - similar to a sugar pill). People that are enrolled in this study will either receive the treatment or the placebo for a period of 90 days. During this time, people that are participating in the study will fill out some questionnaires, and their mental and physical health will be monitored by the study physicians. One of the goals of this study is to also understand whether it is feasible (practical) to do a larger clinical trial using this treatment in this group of people.