I agree with seeing a GI doctor about this. I know digestive issues often 'come with the territory' of CF, but having things written off as inevitable by your dr when it's impacting your QOL so much, esp given it's recently gotten so much worse- is not right. A dr that specializes in these issues would be the right call I think; rather than throwing a random med at you he could determine WHAT would be best and why- and he could also rule out anything more serious causing this.