Is there a chance that you could be pregnant? This could be an implantation bleed. It is about the correct time for this so if this could be the case; it is worth taking a pregnancy test to confirm/rule it out.
It could also be that your period just came a week early, this can happen with a change of routine but you know your body and will know if this is likely or not.
Stress is more likely to make a period late, but there is a chance that your body clock is out of sync if you have had any stress. Even your birth control pills can change things if you have changed to a different type.
If the pregnancy test is negative, I would explain your symptoms to a doctor who will be able to tell if there is any other reason for concern.
Some women are used to periods being late or early, whereas other women's bodies seem to run like clockwork. It is hard to guess without knowing more about you, but if you are worried, it is certainly something to get checked.