Any explanations

I think I got my period yesterday. I am on combined birth control pills and I never missed a day. I haven’t had sex with anyone but I have been stressed for a while that maybe pre cum could have gotten in my vagina while we were doing other stuff since the guy never came. I’ve been stressed for two weeks. I would press down on my stomach a lot and I had really tender breast and headaches and stomach aches. My blood yesterday was ridiculously light which I have never seen within my almost three years of being on birth control like It was very light in color and thin like I could only see it when I wiped and it was barely on the pad. It appeared as brown for the rest of the day and but it was ridiculous a tiny amount whenever I wiped. I understand that periods start off different but I have never experienced that before since birth control or been before that. Today it seems to be a bit more normal but still ridiculously light and I’ve been cramping for two days now. Any things I should look out for or should I be worried?