Why would the lining of my gall bladder be thickened?

I had an ultrasound yesterday to determine the cause of my recurrent UTI's. The radiologist said that I have a gall stone measuring approx 16mm across and that the lining of my gall bladder was thicker than it should be, he said it should be no more than 3mm and mine is 7.6mm. I asked what might cause this and he said it could be a sign of infection, I have looked up the signs and they all mention pain, however the only pain I have been having is in my left kidney due to UTI. Are there any other causes of thickening?