I have been on Levothyroxine for about a month now. Its 25 mcg. STarting to feel some benefits like more energy, skin isnt as bad, etc.. Prior to diagnosis of an enlarged thyroid (levels are "within normal limits" but the doctor still hasnt sent me exactly what they are), I was having menstrual problems- long, heavy periods. I had a D & C in August was was put on BC pills (Yaz) to help keep things under control. The first month was great. My period came exactly on the 28th day, lasted 4 days, not heavy. The next month was a tiny bit more, lasted 5 days. Last month lasted 7 days. The flow hasnt been nearly as bad as before. Anyway, my period is not due for 8 days, and I started today. I have felt like I had PMS all week, but then attributed that to a lot going on in work and at home. Anyway, I am wondering if there is an interaction between the thyroid med and the BC pills. Any experience or thoughts are much appreciated! Since its Saturday, I can't reach my doctor till Monday.