Why is my period so irregular, and what do I do if it comes when I'm on vacation?

Hi. I'm 13 years old and I got my first period in may of 2012. May 5, to be exact. Then I got it again around June 25th (I remember because I had softball tournaments which sucked while I was on my period). Then I got one July 14, and my 13th birthday was on the 21st. Then after that, I didn't get one until September. After that one, not until November, then in late December and late January. First of all, I don't know if I'll get one this month because usually I get very bad cramps like 2 weeks before I start. If I don't, then I'll probably get one next month, but I really can't. I'm going to Puerto Rico for spring vacation with my family as well as some other families. We always go snorkeling in the ocean and go swimming in a waterfall. I really just cannot have my period when we do this, but I might. I can't wear tampons because we're always out all day with no bathrooms, and you can't keep those in for a long time. Plus I've only used a tampon once before and it hurt really bad to take it out. I don't feel comfortable wearing them, that's the bottom line. My periods are very painful, too. What do I do if I end up having it? Can I delay it? The problem with delaying it is that I'm not even sure it's coming. Please help. Thank you.