I don't have answers, but I want to share that we've been dealing with this with my daughter. One GI called it functional constipation and sent us off. We went through three GIs, but have finally found one that is all about getting to the root of the problem. There are LOTS of things that a thoughtful, hard working, smart doctor can try. Some of the things they have planned to test or already tested:
1. check the gut for bacterial overgrowth than can slow motility. If this is the case an antibiotic that stays in the gut (isn't quickly absorbed like the kid used for a lung infection) can clear this issue.
2. check the liver, gallbladder, and pancreas on ultrasound to rule out issues related to those organs.
3. check the thyroid.
4. check for celiac's disease, IBS, and collitis.
5. check for nerve damage.
In most cases they will want to start with issues that are related to CF and move towards ones that are separate diseases all together, since its more likely to have the same disease manifest in other places in the body than to have the same person have multiple genetic diseases (though certainly not impossible -- we've referred to it as hitting the genetic lottery in our visit with the GI).
I don't know if any of this helps, but I hope you will find a doctor who will take this one with you. Taking miralax twice a day and having to do a golytely cleanout once a month is not good QOL on top of eveyrthing you have to do to stay healthy. . . there may be no answers, but until its all checked out, you don't know that and could be missing something that could help.
