Stress could cause that or if you have just started or stopped any type of birth control
I wait just a little while longer and if you still don't have your cycle I would start thinking about going to see your doctor
Well, my first question would be do you usually have a regular period or is it a bit on the irregular side? A lot of things can contribute to a missed period. Stress can affect many things in your body including your period. Also, a lot of exercise, or a change in dietary habits, even weight gain or loss can be a factor. I myself have an irregular cycle and have been pregnant twice. Both times it has taken about 3-4 weeks after i miss my period to show up on a home pregnancy test. I'm not sure if you are having the same issue but I would get a blood test just to ease your mind :-)
doctors say to wait til you are late 5-10 days as the urine will be more concentrated. some people are harder to detect if they are pregnant. you can get a blood test at your doctors to detect it sooner