Missed period on pill

So, the last time I had sex was in August. Since then I’ve sort of gotten my period on my placebo weeks in September and October, it’s just been very light and mostly brown like old blood. This month I didn’t get a period. That has never happened before on my birth control and I’ve been on it for maybe 6 years. Has this happened to anyone else? I’m taking a test in the AM but could it be possible for it to say negative if I actually am pregnant at about 12 weeks?