Another one please anyone help!!!!?

my thing is no period and it's due the 17th so I tested the 19th(hpt) negative,then went to doctor on the 21st negative blood test, by the way had on the 10th...took another test on the27th(hpt) negative what is wrong, and i am not stressing about anything...so am I to early testing,but wont the blood test pick it up. well go to the obgyn can they do any other tests to make sure...still no period and it is the 28th, my period comes on like clockworks i just don't understand please help me!!