LATE PERIOD ?

I am only 3 days late on my period but I have literally no symptoms at all (of impending period OR pregnancy) I am usually very regular and can tell when I am about to start, and I have also been pregnant before so I know how my body acts when I am pregnant, but I'm not getting signs of either one ? I know I should just take a PT for peace of mind, but I just wanted to find out if this has happened to anyone else ? Has anyone ever been randomly late for no apparent reason and how long before you started ? If so, did you ever find out the reason behind being late ?