Sylph, unfortunately, people in mgmt positions and even HR aren't always up to date on the laws, etc (I'm in HR, by the way). I know that, in order to request reasonable accomodations where I work (a university), you are supposed to fill out a form and have your doctor complete to say if the things are medically necessary. Maybe if you were to write out your requests and have your doctor comment on each one as to why they are medically necessary, then they will be more likely to approve them. Plus, if you have doctor's certification saying they are necessary and they aren't unreasonable cost wise, you can always file a complaint against your employer.
Sometimes people in HR positions are very skeptical of requests like FMLA and reasonable accomodation. Providing HR with information on the disease is a good idea but having a doctor certify that it is necessary for YOU will be more effective than providing them with an overview of what Crohn's can do. Good luck!