How can i delay my period for holiday?

I am 14 and i've had my period for around 3 years. The thing is my period always delay, sometimes a month and a half before it returns or 2 months. It also comes at the worst times. The last christmas holiday, school camp, friend's parties. This year we are going somewhere special and i really don't want my period. Mine is already over due a month and a half and i'm going on holidays on the 24th and come back on the 12th. Is there any pill i can take ( i don't take any pills at the moment) or what i can do to delay me period. The thing is i don't know when it's going to come next time which makes it harder. Thanks. Most helpful answer gets 10points :)