Colonoscopy and change in bowel movements

So I have had IBS for a very long time.  In the last few years my so-called bowel movements are anything but(moving).  Lots of straining.  I had a colonoscopy last November.  Immediately, There was a distinct change - Whereas I always have had at least one bowel movement a day, now it's every other day.  Plus they are no longer formed, but rather consist of various sized lumps.  which come out individually, and/or are clumped  together.  When  clumped together, they are much larger than previous movements and nearly impossible to expel.  Prior to this colonoscopy(had 3/4 previously)  - I never
experienced any of this.  I'm very scared.  Colo-rectal surgeon who performed procedyre says it had nothing to do with changes.  I know better.
Anybody else experience these changes after a coloniscopy??  If so, have an explanation, or has previous function been restored??  Also with regard to IBS..have any of you who've had it a long time also experienced a decrease in movement over time, with severe straining necessary??  Appreciate any/all input!