3 days passed missed period

Katherine
Hi everyone, 
I have a question.... I was suppose to start my period on Tuesday and it's Thursday and I have taken two pregnancy test but both has said negative... can someone help me out? How long after my missed period should I take a test for it to come up positive. My husband and I have been trying for 6 months and really wanting a baby to extend our family. Should I go to the doctor? IDK