I doubt that you formed kidney stones in just a few days, but were flushing ones that may have been deep-seated in the kidneys.
I've just experienced the same thing from taking milk thistle for about 45 days. Get my kidneys cleared from this round, and I'll be right back at the milk thistle!
I make a meal out of a raw pineapple at least once a week. This has never given me a kidney problem.