What are things that can cause a late period (that aren't pregnancy)? My period is almost a week late. I am sexually active but use protection every time.

I thought exercise would help bring it on so i went to a zumba class wednesday night but it still hasn't come.

I'm trying not to stress because I know stress can delay it. I'm just starting to worry because last month it was 4-5 days late and now I'm late again. I'm usually pretty regular with it only being a day late/early.

What are things that could cause a late period?