In addition to what Ron said, I would like to add: Have you had bloodwork done? With Crohn's, it's pretty easy to develop certain vitamin deficiencies - in particular, vitamin D, B12, and iron. If you haven't had bloodwork done lately, I would ask the GI to do some bloodwork so that you know what you might need to supplement.
Verify that you are up to date on all of your immunizations before you start crohns meds. A lot of GI's forget to check this. You may want to get a blood titer test to make sure your immunity levels are adequate.