I also was hard to diagnose, as my colonoscopies never showed anything. Finally, a capsule endoscopy revealed what the dr. thought was UC, but my symptoms were that of Crohn's, so it was "indeterminable colitis." They said the colitis was in a part of my small intestines that the colonoscopy doesn't reach, which is why they never found it before. Eventually, they just started writing Crohn's as my dx. I was even questioned by the clinical trial people, when I tried to get involved, as to whether or not I actually had Crohn's (they weren't sure I did), as I don't have one of the biggest symptoms: D. I always had the opposite problem. Anyway, my new GI doc said that he has had some patients with Crohn's that never exhibited any GI problems at all, that they had arthritis problems and tests indicated Crohn's. So, from what I have researched, know from experience and was told by my doctor, yes you can have Crohn's, even if the colonoscopies aren't showing anything.
...rejoice in our sufferings, because we know that suffering produces perseverence; perseverence, character; and character, hope. Romans 5:3-4