Confused

I know I'm due for my af this week but now not sure exactly when. Since this is my first cycle using glow I only had put this cycles info. So I was bored and decided to go back starting Jan and noted my af for every month now my expected date of af changed 2 days earlier than before so now I'm due tomorrow 9 /14 instead of 9/16 and I tested earlier today and got a bfn.