Sorry your Dr was so rude! I also saw a rheumatologist because of persistend lower back pain. My Rheum. DID say that UC can cause arthritis, but did say that the severity of the pain would vary on whether I am flaring or not. She said that during a flare the pain could be worse that when I am not flaring. If you are flaring currently then that might be the pain. I'm not sure about
the kidney stones, though as I have never had one, thankfully! Is the pain really low in your back close to your butt or a little higher where your kidneys would be? If it is higher then it might not be the arthritis, but your kidney stone moving like you said. Sorry I'm not really much help. Hopefully someone with better advice will come along!
I hope you feel better soon!