Questions

Okay so my cycles have been regular for pretty much ever. AF always came on the 16th then last month I was 1 week late exactally. So this month I used Opks I O'd on the 13th of this month according to glow AF is 2 days late when I pushed my period back a day cause it still hasn't showed glow sent me this things saying when my periods "late" I should still expect it so question is why would glow put my period for the 21st if it takes 14 days for LP and if that's true then AF should arrive on the 26th .. But my periods are always so regular till last month