Hi there,sounds like me before I started Imuran,which has been ,oh about five years,and knock on wood,no problems since.
Perhaps it's a sign of a stricture. How are the #2's coming out? Does your stomach get bloated? Maybe the digestion is backed up and the body is trying to alleviate the pressure by pushing the food out the way it came in.
I'm dealing with something similar and this caught my eye.
Hope you feel better.