Late period negative test never missed a period

No added stress, no new medicines, no birth control had sex close to the beginning of period due date like a week or two. No spotting no period but I have a negative test. I've never missed a whole period in my life. I've been late a day or so a time or two but never a whole period. Somebody have any clue what could be going on? I also just had labs done two weeks ago and everything looked great health wise so I'm not sick or have any medical condition.