Is it normal for my kidneys to hurt?
When fasting you need to drink more. I personally noticed it and making sure you drink more water is best. I use a Soda Stream to make it easier. Carbonated and flavored with no calories. Or you could buy cans of flavored seltzer. Just make sure it has no sweeteners, just water and fruit flavor.
Drink 4L a day. Depending on your weight/activity in the day might have to drink more. That’s an average for around 150/160 lbs person that mostly sits down.
Sound alike a lot but it really is needed. I try to hit that and I drink black coffee in the morning (not counted towards 4L. Definately helps. If the pain continues when you’re drinking enough, then go see a doctor.
Carbonated water is great too so get a soda stream or something if you like carbonated water.