Confusing notification from Glow..

Hey ladies..

So I just got this notification a little while ago.. I was due for my period the 16th of Sept, but as of today, still nothing.. I am 15 days late, but negative tests (only did 2, one on the 18th and again on the 30th).. Idk if its because Im not using FMU or having drank before testing that is giving me a negative test, but more then likely not..

So if Glow is saying I should start my period today, does that mean from the 16th (when I was due in Sept).. If so, that is odd because it would be a very short time from the 16th of Sept up until today for me to get a period, if it did show up today.. That is extremely confusing and not sure I understand.. Can someone help explain that? TIA!