Suggest Medication To Delay Menstruation

hello doctor, i am 26 years old. my query is regarding postponing my periods. my due date for the month of november was on the 25th; but i have not had my periods yet. its already delayed by 8 days. i am getting married on the 12th of december and i would like to postpone my periods so that it would not interfere with the poojas and other rituals that may last till the 23rd. please suggest which drug i could take and when should i start taking it? is it already too late for me to start the medicine? would it be 100% effective?