** Thanks for contacting with your health concern. 1. As the pregnancy test is negative [twice] with no positive signs of pregnancy but periods are missing [on a due date], thus it can be upsetting and confusing, so it could be due to certain lifestyle changes which were done recently [if any] like: - excessive stress - loosing or putting too much of weight - heavy exercises - suffering from PCOD [polycystic ovarian disease] or having a high level of prolactin [hormone] 2. Another commonest cause is functional ovarian cysts which will prevent bleeding so get an abdominal USG done to exclude the same. PS. since UPT is negative so it is best to seek suggestion to know why you have missed your periods, a Gynecologist would be ideal to consult, for appropriate examination/investigations.