Does Unwanted 72 Affect The Regular Menstruation Cycle?

hii...my period date is 5th day of every month and i plan to have maintain relation with my bf on 18th day without any protection 2 to 3 times and in that case if i will take unwanted 72 within 24 hours then is there chance of pregnency ? and also how it effect on my regular periods but i will take this tablet once only not next time or not in futre. please guide me