Birth control

I started taking birth control pills for  2 months since I had my little one on April 15 and I have basically been spotting for 2 months on and off. I suffer from endometriosis so my OB wants me to maintain that under control by having me on a low estrogen pill but I was wondering if you all are on the pill which one do you take maybe I'm taking a bad one? Mine is: Sronyx.