Sorry to hear about your latest bug Taz - you do seem to be really run-down at the moment. Hope you get a date for a scan soon so they can sort out whether you have a kidney stone or anything like that.
I haven't suffered from anything like this myself but my husband had recurrent kidney pain over several years and he suffered very badly - with intermittent sickness, nausea and severe pain until an operation in the summer cured the condition he had, and he has been well since he recovered from the operation, so I do sympathise.
In the meantime keep drinking! I understand some brands of tea/coffee are decaffeinated gently/naturally so should not contain chemicals likely to upset the stomach but I can't find any info on this! For instant decaff I used to drink Cafe Hag because it said it was decaffeinated naturally but seem to have lapsed recently and not sure if it's still available. I drink Taylors Decaff ground coffee which is decaffeinated using the water process. Sorry this is a bit off topic but in case you were desperate for a coffee!!
Hurdity x