Hey
I guess I am really lucky with my work as my boss and the guys I work with are really supportive.
It might pay to gather a whole bunch of information on crohn's that explains the conditions the side effects etc and sit down with your boss and even your co workers and discuss the condition with them as best you can.
It may well be that they don't relly understand the condition and what it is and how it affects you. The more detail you can go into probably the better as they may never ask you about it again, well that's what I have found anyway.
Good luck
Also if you are on Facebook, look out for some of the forums and groups on there, as they can be very helpful with ideas and the people are all going through the same things as us.
take care
Maree