What Causes Delayed Period And Darker Nipples While On Loestrin 24 Fe?

I just started Loestrin 24 Fe 1 month ago, I'm barely into my second pack and I still haven't had my period. My doctor put me on this pill because I most likely have polycistic ovarian syndrome. I have had unprotected sex since being on the pill but my boyfriend pulled out every time and I haven't missed taking a pill yet. But, I have noticed my nipples are a bit darker which is a sign of pregnancy, but I also heard that can be from taking birth control. I'm very worried but I feel like there's no possibility I am pregnant. Tell me what you think.