I HAD the exact same issue with the OP and tried everything. Nothing worked to my 100% satisfaction until came upon the idea that perhaps I should make my lower back muscles stronger. It didn't take much. Just a steady exercise of 30 minutes on the eliptical machine three times a week solved my problem in less than 4 weeks. These are Not the ones where you sit down and use your feet only, and not the typical treadmill where you are either walking or running - those are great for your overall health, however. Ellipticals actually elongate your strides, the action which provides stretching AND flexing your back as you keep your feet on the pedal. Think of it as a forced Thai massage on your hamstrings and gluts.....

Otherwise, it's weight training using things like hyperextension movements and sit ups and whatnot. But that takes longer time and higher impact, not to mention needing correct equipment while we all travel. However, I find that hotels typically have elipticals even at two star bare bones places.

ps. you should keep the "slope" or "stair height" setting at one of the lower levels. This works the back muscles more.