Please help!!

The last few months my period has started between the 6th-8th. Mostly the 6th. Its now the 10th with no period. Ive taken tests up through last night and gotten negatives. Any advice? Has this happened to anyone and they were still pregnant?? Any advise would be so much help!! I'm not terribly stressed either so I don't think it's that. Besides...That's a WHOLE missed period.