Ladies, my period is 10 days late but I went to go get a blood test when I was 7 days late and it was negative, all pregnancy test have been negative too. Last time I tested was tuesday. I'm on cycle day 36 and my cycles are never over 27 days, my period is never late. What is going on? After a negative blood test is it 100% sure that I'm not pregnant?? My sister has had blood test be wrong for her, they said pregnant and she wasn't and then not pregnant and she was. I would appreciate you opinions. Have you girls had a blood test be wrong??