Had constipation probs over 15 years recently after having gallbladder removed became much worse & accompanied by middle back pain. had ct scan after surgery at the er because of constipation. showed no block but stool not moving. what could it be?

One side effect of abdominal surgery is constipation which is exacerbated in your case. CT isn't a video so it can't tell your stool is moving or not but I think it shows significant stool material through out the colon. You just need to use laxative such as miralax OTC as needed until you have good bowel movement and then resuming your previously baseline regimen for tackling chronic constipation