Hey John-
First of all, hang in there. I know it can be tough spending so much time in the hospital. Mess with the docs and nurses a litle bit to amuse yourself.
To answer your question about who to believe...you beleive the person who can prove it to you. Have you had a colonoscopy? have you had surgery? Are you just being "observed?" If they haven't looked, they can't tell you for sure what's going on, so if you haven't gotten a colonoscopy yet, that's what you should be pushing for.
Good luck...and keep smiling!