Confused about when I'm due on?

Emily
HI ladies, both my apps said I was due on today, and I had bad period cramps last night  and much to my surprise I didn't wake up with AF. I think I ovulated on the 6th of November and bbt would also agree. I tested and was negative with fmu, when shall I retest ap now says I'm due on on the 24th!?
Plus about to do night shifts when is the best time to keep temping? Help greatly appreciated