What Causes Pain In The Flank?

Hi, I have left flank pain that has coming and going for the last week or so. I do have a history of kidney stones, infections of both bladder and kidneys, IC since I was diagnosed at 19, IBM and Fybromialgia. I had an ultrasound today, an abdominal one, and I am just wondering, the left side was so sensative when the tech was doing the US, that I was gritting my teeth for the whole 30 minutes it took. If it is that sensative, on the left side flank (throbbing in the black left flank, and tender in the front) Is this a sign of yet another stone? I also have no fever, but am flushed looking, with red blotches on my arms and chest that are hot to the touch.