I'm late.

Well, I always start my menstural cycle at the end of each month and it usually continues into the next month. This month I am bout 3 or 4 days late so far. I have a period app called Clue I have been using almost this whole year. Clue says Im suppose to start today(october 4) or 5. But. This one says I was suppose to of started last Thursday or Friday. I have yet to start... Also, I usually get cramps bout a week up til my period but I havent had any. I only remember of one day last week when I had cramps for a lil bit. I took a test last week but it said not pregnant. Any advice??