I'm 16 days late for my period. i've had a little spotting, but every test i take has come back negative. ?

It happens sometimes: In a woman with regular periods, some causes of a late period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (like hormone or birth control pills), hormonal imbalances, etc… Seeing a doctor is a good idea if symptoms are persistent, recurring, or worrisome. Home pregnancy tests are very accurate by 3 weeks after sex.