I have sex on 6 th nov but on that month I have my periods on time after after 11 days, but on next month i.e. dec till now I didn't have period and I have been late by 2 days why?please help I'm tensioned

Stress, changes and different things can make it vary. I heard a study one time that they can change according to other women's that you hang around. Like if you go from living with mom and sisters to a dorm room mate.

You could well just be stressed out and that is keeping you from starting your period. Relax and have some hot ginger tea. Ginger helps to bring on your period when it's "stuck" in there. I wish you the best. :)