My period is late

Hannah • Me & my SO are actively ttc baby #1 🤞🏻🙏🏻✨
Okayy so glow said I was to start on the 16th but af is a no show. No cramping no signs of af anywhere. I was 4 days late last month. I don't know if glow is wrong or what? Not sure if I should be concerned or not. Ugh why must mother nature be complicated :( help...