Early period despite pill

[crappyday]

I'm on the pill so usually period every 28 days.
My period has arrived a week early . I'm under a massive amount of stress at the moment- is that the likely cause? I'm so cross- having a period this week is very inconvenient. I haven't missed any pills.

Do I need to check it out with doc or nurse? Or just presume it's a one off...

Have you taking any pill later than normal? If taken later than usual then breakthrough bleeding can start.