Everyone's bodies are different. There is not something that you can do non-hormonally at least, to regulate your period. One option is to get on oral contraceptives. This is the only true way to regulate your period. Not everyone is on bcp's for their sexual behavior. Some women simply like how it regulates their period. You would need to see a health care provider to supply you with bcp's. This is an option though and keep it in mind.
Natalie

Your doctor can give you pills that will delay your period up to ten days. People use it for events such as yours. Vacations, wedding nights and so on.
Birth control would help regulate your period in the future, but if you don't want it on your upcoming trip your doctor can give you the pill I mentioned above. I really don't know what it is called though, but they will be able to tell you.

I can give you one reason why sometimes a period becomes irregular all of a sudden, is if you start work in a new place where there are a lot of women, or starting spending a large proportion of the day with someone new. One of the things that happens is that women in a group often find that their periods become synchronised, maybe one of the women has a stronger hormonal charge or something like a sort of "alpha female", and everyone else gets thrown off slightly by a couple of days each month, until all the girls in the group are more or less in synch.

I don't have an answer to your problem unfortunately (aside from bc pills as already suggested, where you can play with the dates a little by stopping or starting packets early), but it might be a reason why you became irregular?