I used to be prone to cystitis, in my twenties and thirties, and passed a kidney stone once that was extremely painful. I also used to be someone who took a lot of vitamin C...believing it was really good.
I have not had kidney problems since beginning to drink cranberry juice, ( just the pure concentrated unsweetened kind you buy at a halth food store and dilute to drink) and eating cranberries. In winter I frequently have green or herbla tea in which I put about seven frozen cranberries. They cool the tea, and I eat them after drinking it. I no longer take supplemental vitamin C. but I have been drinking lemon with water for about ten years. That, along with being vegetarian, and now almost purely vegan has all but eliminated what used to be a recurring irritation.I was always on the edge of a UTI.
Cranberry juice is Queen! when it comes to kineys and the urinary tract.
Better the real food than the supplement they extract from it...
One thing I found really good for kideney stone attacks (I lived where they did not have sonic equipment to 'break' the stones)is the homeopathic "equisetum".
(horsetail) It did something that enabled the body to partly dissolve a large stone and pass it. (About the size of a kidney bean.)