First, go ahead and be angry. It's OK. Crohn's sucks. Cancer sucks.

I think the important thing is to see anger as a transition. Let it happen — even embrace it for a while — but think of it as a vehicle that's taking you from where you were before to where you'll be in the future. It's a bumpy ride, but the ride isn't your final destination.

If you're finding the anger too hard to live with in the meantime, obviously working with a professional therapist is the best choice, but if that doesn't work for you (due to preferences or finances), there are therapies that can be very effective for many people when self-administered, like Cognitive-Behavioural Therapy (CBT) or Acceptance-Commitment Therapy (ACT).

The original CBT book was "Feeling Good: The New Mood Therapy" written by Dr. David Burns 45 years ago. It still holds up fairly well (it helped me get over chronic anxiety 20 years ago), and has actually been through multiple clinical trials that have demonstrated that it has efficacy the same as or better than medication for many situations.

There have been many more resources published since then, of course. What they all help you do is break down the anger so that it's no longer a tidal wave threatening to drown you, but something you can examine, understand, and even have a pseudo-conversation with.

Best of luck!