Thanks for the query.
Some amount of fluctuation in the menstrual cycle is common.
The period can get delayed due to many causes like stress
and strain, weight changes, poly cystic disease, thyroid
If there is any possibility of pregnancy
better to rule out that first.
Then you wait for one more week, possibly by that time you will get your periods. If not consult gynecologist get examined to find out the possible cause for delayed periods and take treatment for withdrawal bleeding.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429