The first thing you have to do is relax! (I know this is easier said than done!) but stress can make the body do funny things, including delaying your period.
My suggestion is go buy a pregnancy test, I think they work for anywhere after the day of a missed period. If you get a negative result and still don’t have your period about a week latr, test again. And then if you continue to feel the way you do right now, I’d go see a doctor. This is what I did, and he gave me a test at the clinic, and sent me for a blood test to be sure.
Make sure you take good care of your body in the mean time, and good luck.