I guess that is the nature of HA, thinking the worst of any little health issue---you have to somehow learn to stop doing that. Maybe you could write down on a piece of paper all of the minor reasons you think you period hasn't started yet, like stress or anxiety or just a normal hormonal fluctuation. Don't write down the catastrophic reasons you think it's happening, and just focus on those minor reasons.....tell yourself these things are highly more probable than what you're thinking is causing the issue. If you start to think this way you will be able to calm yourself, calm your stress, and the bonus may be your period will start!
Take Care :)