What Causes Delay In Menstruation Other Than Pregnancy?

Hi please can you tell me why my period is a week late, could it be down to me being ill,24hr bug (all family got it ), i know i'm defo not pregnant cos my husband has had a snip 7 years ago and i have done a test already, negative. Have recently got married and dealt with alot of stress. please can u help just for my piece of mind thanks