The only way I've ever been able to get through trips like this is being honest with my boyfriend about the problem and asking if he can give me some time in the room alone. It's really awkward discussing it but even though no one I've dated has fully understood the problem most have been understanding enough to give me time I need.
Another technique I've used is to turn the shower on or play music in the bathroom, so they won't hear me using the toilet.
I find suppositories don't work if I'm really stressed and anxious about going, and likewise get horrible cramps. If I get into a really desperate situation then I try and book a colonic, which usually gives a couple of days reprieve, but it's an expensive 'solution' and not always available depending where you're going.