Why My Periods Are Delaying?

I am 24 and since I can remember I have always had regular periods but for some reason,I am 7days late this month,I am not sexually active and yea mayb I've been under a bit of stress lately but I've been way more stressed and I still get my periods,I'm trying not to freak out too much,Pls help me,what do you think is wrong with me?i should state that I got my normal pre-menstrual symptoms such as pimples on my face and my breasts getting bigger but no period.Pls help me!