First find out if they think you have a stricture.
I did not have a stricture but I do want to say that I have that problem too especially my first month when I was on the low residue diet. (I was just diagnosed 08/03/07)
What finally worked for me was to take colace/docusate for 2-3 days in a row and then something started happening. I also agree that water is very important even if you are on a liquid diet. (i drank 8-10 glasses of water on top of soup, jello etc and STILL nothing was happening but atleast I could say that i was well hydrated. Unfortunately, the longer that the poop stays in your intestines, the drier and harder they get and the more bloated and icky you will feel. I actually got to the point where I was nauseus and felt like vomiting.
what else did I do. I also took and still take metamucil supplements and once I was able to, started eating soluable fiber like oatmeal. If worse comes to worst, I take milk of magnesia but I have only had to do that once since I was diagnosed.
I am slowly intergrating more fiber into my diet but I personally still swing between constipation and diarreah all the time. At first it used to freak me out because I never had a problem with this before but now, I'm getting used to listening to my body and making adjustments as necessary. You might want to ask your doctor how many days you should wait before getting worried before having a bowel movement. I believe my doctor told me to go to dr if I went 5 days without having a bowel movement UNLESS I was having increased and severe abdominal pain.