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A CT scan does not indicate tissue that is causing pain, but it can show tissue that is inflamed, because inflamed tissue tends to be swollen, which is able to be seen on the CT scan. There needs to be a certain amount of swelling to be detected by a CT scan, so it may not detect mild inflammation. There is also certain tissue that is not seen well by a CT scan, but it will detect many areas of inflammation.
I would also note that the fact that this symptom did not start until a few months would make it even less likely that it was due to the colonoscopy. In the rare situations in which colonoscopy does cause pain such as you describe, the pain typically starts much sooner after the colonoscopy.
There is significant variability int eh length of the mesentery, so a CT scan would not detect stretching of the mesentery, but it would detect inflammation, as noted above.
There are certain situations in which inflammation can persist. Pain can occur from scarring, but most scarring is too small for a CT scan to detect. The appropriate specialist to evaluate persistent pain in the abdomen is a Gastroenterologist, although you might want to consider seeing a different Gastroenterologist to get an unbiased opinion.