I had several colonoscopies, sigmoidoscopies and finally a endorectal ultrasound for a stricture in the sigmoid colon. The operative procedure report stated that there is thickening of the mucosa at the site of the stricture. As well, the submusoca and underlying muscularis is thickened. Plus it said thickening a couple of more times. In my case this led to a resection as the stricture was made up of scar tissue.
I question your doctor saying he didn't want to create more problems with a heavier medicine when the colazal doesn't seem to be working. There are problems that could be happening without getting the inflammation under control. Doctors have different opinions on their approach. A sigmoidoscopy should help tell you more.