6 days late, negative test but feel like something is going on

My period is 6 days late and trying to get pregnant through a sperm donor, I have been pregnant many years ago and didn't get a positive result until I was 2 weeks past my due date for my period but I felt cramping for majority of the two weeks (not realising I was pregnant at the time) this time around there is cramping that comes and goes and I get stabbing pains in the left ovary never had that before, I did take a clear blue digital test and it said not pregnant but I feel that I might be, anyone experience a false negative but in actual fact turned out to be pregnant?