What causes your period to be three days late?

There are many factors. Stress and amount of exercise/activity can affect the timing. I would say stress is probably the factor. If you are a week late, you may want to take a pregnancy test. Many things can cause this. It could be stress, pregnancy(dont automatically think that) Change in diet or excercise..an etc...Give it a couple of days before you begin to worry If you have never had a child before, I don't think that it is a big issue. Women tend to have irregular periods until they have their first child. I have never had regular periods, but I have checked out to be healthy and normal. I have actually gone 2 months without a period, but according to those I asked, there was nothing wrong. If you have had a child before, it is normal for your period to change a little if your lifestyle has changed.