Hi there, the pain in your back is due to holding it in yes. 1litre in an hour is quite a lot, you should maybe space it out a bit more.
On the peeing front I can totally sympathise, my job involves driving and spending time in other peoples houses who dont always have the cleanest of loos

so it gets very tricky sometimes. To be honest I get really fed up with going to the toilet so much, it sometimes puts me off drinking but I know that is silly and will affect the diet.
Please be careful minor kidney problems can lead to major ones later in life..xxx