Hey :)
I too suffer with kidney issues. Having a duplex system on one side causes my issues. If sex is more vicious than normal it can cause an issue l, I find taking nurofen before helps.
Medicals professionals say cranberry juice works but it doesn't, it feeds it imo coz of the amount of sugar in it.. Minerals and fruit juice esp apple causes issues for me too down to how acidic they are. sugary foods cause issues for me too esp if I've drank alot in the day before sex, sounds odd but definitely does...
I really hope u get sorted... Kidney pain sucks x