Dominico,
Oh My Goodness!! You have just explained my symptoms exactly. It's always if I sleep for then 6 hours, mostly on the weekends (because I can never get to sleep at night on the week days and only ever get 4-5 hours of sleep). The pain is pretty severe. After going to the bathroom it will slowly fade away. I've had this go on for a very long time, but finally today I thought I should look it up. How strange! I saw on another site that it could be from sleeping funny. But I don't sleep funny. I lay down on my back and almost always wake up in the same position. If I do change position it's for the minutes between my alarms, I roll over.
I do have intersatitial cystitis, which causes painful bladder, but I don't know if it causes back/kidney? pain that severe.
I know you posted this a year or so ago but did you ever get any answers from your doctor?
1. When I eat heavily at night before bedtime
2. If I eat a lot of sugary foods at night before bedtime
3. Drinking lots of water throughout the day makes it go away
Drinking raw/unpasteurized milk is dangerous. The risk of bacterial infection far outweighs any purported benefits. I know there are a lot of vocal and adamant proponents of raw dairy out there, but please consider that their claims may be wishful thinking, and that without heating milk to kill bacteria you are rolling the dice every time you consume it.
I seem to have exactly hat you have... :-(