Your period could be late due to stress or hormonal changes and sometimes can mimick pregnancy symptoms if you are stressing that you are pregnant or you could actually be pregnant. Test in a few days and see what happens, if you get a negative then test in another week, if the same results schedule an appointment at your doctor for a blood test.
Take the test when your period is 7 days late. I took one the day I expected my last period, it was neg, took one a week later because I still hasn't gotten my period, positive. Also if you don't have regular periods, it can make you worry.