I've been off a week....

Bee • ♥️
So I came on my period on 16th Nov.. And finished 22nd.. Now I'm back on my period today (30th) ... I'm confused as my periods are normally on time and if I'm not on the day <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> says it's the day before or the day after 
I don't understand