Suggest Methods To Delay Periods

Hi Im going on holiday on the 14th august 2011 for one week back on 21st august, I told my doctor I wanted to stop my period or delay my period and gave me norethiserone but the thing is Im really rubbish on keeping track of when my periods start have no clue doctor told me to take it 3 days before my period. Do you think it would be ok if I took them week before I go on hoilday? Then ill be on the tablets for two weeks then stop the tablets on the 21st august last day of hoilday.