Two negative pregnancy
tests rule out pregnancy.
Although you have ruled out change in schedule,sickness and change in your wright but still there are other factors like stress
or some medication or being near to your menopause
,which may contribute toward your delay of periods.
Wait for a week more and if you still don't get it,you may have to consult a doctor to get examined and prescribed some medicine to get your periods regularised.
Just relax.Every thing should settle soon.