Birth control question.

Hello! I've been on the pill for almost four months now. I am taking trinessa. Which I'm pretty sure is a combination pill. I've always gotten my periods on the third day of the placebo pills. I'm sexually active and don't use condoms. So, today I got like brown blood in my underwear and its the first day of my placbo pills. I'm confused. What does this mean? Two days ago I took my birth control about 7 hours late so maybe that's it? I don't know! Someone shed some light :/