What Causes Delay In Periods? Suggest Remedies

hi i have missed my period since 8th november and last period was on oct 8th.my pregnancy test is negative i have tested 2 times in november month end .Doctor was advised me to take meprate 100mg.ihave taken these capsules for 5days from 8th dec to 12th december but still i am not getting my period ..what to do i am in great confusion what happen to me when will my period will come?