Good question. People with Crohn's tend to metabolise things differently, because of damage done to the intestines.
Perhaps a naturopath? Or practitioner of integrated medicine, like Dr. Leo Galland in New York?
Some practitioners of integrated medicine think that a bad reaction to meds could, in fact, be an allergic response caused by yeast overgrowth. They might treat this by putting the patient on an anti-yeast diet and Nystatin...not permanently.
A lot of theories about treating Crohn's, especially dietary ones, revolve around the issue of overgrowth of bacteria or yeast, and trying to control this overgrowth.
The SCD diet seeks to achieve a balance, overall, between good bacteria and yeast.
Because you do have asthma, it does look suspicious for allergies. You can check out a book, "The Yeast Connection" to get more info. Dr. Leo Galland's book, "Power Healing," is a great overview of nutritional issues and some of the failures of conventional meds and practises.