There are 2 options. Going on the contraceptive pill leading up to the holiday, and then not skipping a week of your pill for the time when you would due your holiday. That, or use tampons and that way you can still go in water and wear bikinis etc. Maybe something to talk to your mum about and see what she suggests.
The only way of postponing menstruation is by birth control hormonal pills. A traditional pack of birth control pills contains 28 pills, but only 21 are active and containing hormones. the rest 7 are inactive pills and when they are taken bleeding occurs. When you do not take these pills then menses get delayed.
The other method is by taking progesterone only pills like Norethisterone. It is usually started two- three days before a period is due and then taken for the next seven days and then stopped, when normal vaginal bleeding will take place. You can talk to your gynecologist and get it prescribed as it is better to take it under medical supervision.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.