Haven't started!

It never fails. I always start the day before the glow says I'm going to start.. This time it's different! <a href="https://play.google.com/store/apps/details?id=com.glow.android">Glow app</a> says I should start today but I haven't and I didn't yesterday (when I usually start) I took a prego test Thursday and it was negative? I have been cramping like an full force period mode! Any suggestions?