Normal blood work doesn't automatically exclude active disease. Check out the last few posts in this thread
to see what I'm referring to. To definitively rule out Crohn's, you need to look at all
the bowel, not just the colon. That means a small bowel examination on top of a colonoscopy, or the pill cam.
Re the steroids, not everybody responds to them. Some patients are 'steroid-refractory', which means basically they don't respond to them. I have to say, 30mg is fairly high, but you might possibly do better at 40mg, which is the standard starting dose for a course of steroids. Unfortunately 'cos you've already been at 30mg for a month, I'm not sure it would be a good idea to increase the dose now. Steroids are not something you want to be on any longer than you absolutely have to, really.
At any rate, it's extraordinarily unlikely to be bowel cancer at your age.
Edit: Well late with my reply - it seems irrelevant now, oh well :/