positive home test, but negative at the doctor?

Breeann

so yesterday i got a faint positive with a blue dye test. i showed up at the 3 minute mark. i had a pre existing doctor's appointment this morning. i went to the bathroom around 7am and again at the dr at about 10:30. but the test there was negative. my period was scheduled to start today. has this happened to anyone and them be prenant?