If the CT results were looked at by an untrained eye, a
kidney stone could have been missed. Not all types of
stones show up on film, and when they do, they appear as 'shadows' and can easily be mistaken for bowel gas. Have your results read by an actual urologist, not your PCP.
My particular type of stone (Cystine) don't show on x-rays, KUB's, IVP's, or CT's, but the trained eye of a nephrologist or urologist can catch them (they know what they're looking for).