I had my period on 21st July which lasted 5 days which is normal for me I have an average 35 day cycle so I ovulated round about the 30th July. My next period was due 14th August. It has not arrived I'm now 5 days late I've had no bleeding, minor cramping and a touch of backache. A online pregnancy calculator calculated if pregnant I would be 4 weeks pregnant by now. I've took numerous pregnancy tests, different brands and all have come back negative. Any one else had this problem?