What causes kidney pain?

Hi doctor,

I have just started fasting from yesterday morning and last night I was having slight kidney pain. Then I awoke in the middle of the night with some kidney pain and a swollen kidney feeling and urinated with difficulty like having to really push it out. Similarly, last year my kidney got worse when I was fasting. When I was under 1 year of age, I had an operation on my kidney and have a large scar in front of the bladder or abdomen area. It was a blocked urethra, which caused whatever fluid back to the kidney causing damage. They said that my kidney would have to get removed at one stage in my life and 21 was the oldest patient in the past that lasted before removal. I am now 30. My height is 6 feet and weight is 187 pounds. I wanted to know if it would be advisable for me to stop fasting and if so would that be for the rest of my life?