Missed period

So according to the <a href="https://play.google.com/store/apps/details?id=com.glow.android">glow app</a>, tomorrow should be the last day of my period....except my period never showed up and I have no signs of it coming. I've had a headache, my nose is out of control and my lower back has been hurting in the evenings. I took a test today and its a big fat negative. I'm soooo annoyed 😔