Dang, that sucks. I've only had a couple and they were awful.
I know this sounds like one of those "one weird tip" things, but it wouldn't hurt to go to Lagoon or whatnot a couple of times a year to try to shake loose the little ones before they grow big enough to send you to the ER.
"Got kidney stones? Ride a roller coaster! Study shows it is the most pain-free cost-efficient way to pass them," say the Mail Online of a study carried out in the US which tested riding roller coasters as a way of passing kidney stones...