stress could cause your cycle to be late, I would suggest that you wait a few more days then take a another test using first morning urine then if that says negative and you still have not started your cycle I would go to the doctor
and yes dont stress your self that can delay you periods.
did you had unprotected se* after your cycle,if yes than i would tell wait for a week than take one more hpt,but still negative than take blood test that will be more accurate to know are you pregnant or not.Good luck. hope this help