Very confused ughh

Amber • Hello I am a stay at home mom, I have two great children a boy and a girl I love my little sweethearts and exp baby #3
So just went back and tracked my cycle days on glow, it says I'm on my 30th cycle day and says my period is suppose to start in five days but last month my period started the 13 and only lasted for 4 1/2 days this month glow is telling me my period will last for 10 days I'm very much confused, could glow be off and could my period be late?