My period is late

Hannah • Me&my SO are actively ttc our #1 baby. Been together 3 1/2 years and have three fur babies Duke(3 1/2)Harley(3) Daisy (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...