Since I have been using this app my period is always on time on the day it says always ! This month it was due on the 16th and I have not got it yet ! I tested twice and both negative . I normally get period cramps a day or two before my period but I've had them for two weeks now and still no period ! Same thing happened when I was pregnant with my son three years ago I had terrible period cramps for the first few weeks pregnant ! When should I try to test again ???