What Causes Delay In Menstruation Other Than Pregnancy?

hello, my menses cycle is 28 days.from past 2 months i have been getting my periods on the 10th of every month.in feb i got my period on 10th and i had sex on the 14th and 15th without using protection.its now 9th of march according to my cycle i'am supppose to get my periords tomorrow but from 3rd march i have been eating papaya and yesterday i started taking medicine to prepone my period.but its 9th of march today and i still didnot get my periods.please help.