Late period....

Is it normal to have all period symptoms but not bleed because of stress ? My period iz 1 week late now... People are telling me it could be due to stress but my period has never been a week late ever. Ive been using period tracker apps including this one for over 2 years and im almost always on time if not ill sometimes be a day early or a day late! But ive also had unprotected sex for the past month. I don't feel pregnant though ?? Just want to know how late its possible for a period to be due to stress ?? xx