Advice... Big time yoyo dieter!

I can't give you any tips to stay motivated to lose that much that fast, because I would be miserable in that situation and not be able to stick to it myself.

It is not really realistic to expect to lose 42lbs in 17 weeks, that's more than 2 lbs per week, which is very aggressive if you're not morbidly obese.

Often when people yo-yo diet, it's because they try to do too much too fast and never learn how to just eat like a normal person at a healthy weight. Perhaps setting a more moderate goal will help you to stick to your plan and not just gain it all back after your trip anyway. Losing aggressively fast also risks more muscle loss, which can lower your calorie needs (meaning you have to eat even less) and perhaps affecting your physique when you get to goal.

Check out these posts, and whatever you decide to do, best of luck!

https://community.myfitnesspal.com/en/discussion/818701/the-myth-of-motivation-and-what-you-need-instead/p1

https://community.myfitnesspal.com/en/discussion/1080242/a-guide-to-get-you-started-on-your-path-to-sexypants/p1

https://community.myfitnesspal.com/en/discussion/10084670/it-is-unlikely-that-you-will-lose-weight-consistently-i-e-weight-loss-is-not-linear/p1