What Causes Delayed Period While HPT Is Negative?

hey, i have a question my LMP was oct. 28.2010 and i have been to the doctor when i was 8 weeks late and taken blood test and urine tests. both negative. they also check for thyriods and UTI everything all my test were stable. i have taken about 5 hpts all NEG. so today im 10 weeks late and still no period. where do i go from here?