The cheap test are not as senstive as the brand name test. I do not know why. You can always ask your doctor to send you for a blood test to see if you are preg, you may have your days mixed up and may have ovulated later than you think. It takes a bit longer for HcG to show up in your urine. That is why it is best to take a preg test after you are already late. I would not worry about it. And you can get AF cramps when you are preg.
No i did some ovulation tests and I know when I ovulated and so worked it out from there and should of got AF on Saturday - still nothing today! did one of those cheapie test this morning still negative! Will leave it till weekend now! I have been so hungry the last few days it is untrue!!!