maybe you tested too soon give it like a few more days and test again to see if you are or not or you could be stressing yourself out worrying about your period being late so relax give it a few days and test again and if you feel that the test are wrong a quick trip to the gyno will ease your mind
You could be just stressing your self out to much and thinking about being pregnant to much.. that can cause your period to be late.. give it another week and take another test.. if its still negative and still no sign of your period go to the doctor, that's your best bet :)