When I looked into disability last year, I went to the Social Security Admin website (I'm in the US) and Crohn's disease is listed as a condition which is considered a disability. I was able to get an immediate estimate of what my payments would be etc. I'm certain that one would need a doctor to certify that they have Crohn's and that it's a severe case, but if you have a doc saying you're permanentely disabled, it doesn't seem like they should be denying it- that's what that list is for.
Also, CD isn't ALWAYS a disability, as stated above. At the moment, I am able to work without issue as I am in remission. At the moment, CD is the least of my problems...it's fibromyalgia that's the current bane of my existence.
Have you seen what your doctors are saying? Have they stated your situation is permanently disabling?