sorry for the bad news but, now that you know your headed in the right direction.
I am the mother of a 13year old with Crohn's and Ceilac. We were told in August also that she had both through colonoscopy. All of this came about because of anemia........
To answer some of your questions: Yes - all are autoimmune. My understanding is Colistis - effects the large intestines-rectum. Crohns - effects the whole or any part of the digestive tract. both diseses have some serious consequences if you dont treat them. Including, the chance of getting more autoimmune diseases.
for now we are lucky she is responding to the meds trying to keep the crohns under control but, it does take time. As for the question is this common? Our doctor said NO but after being on this board there is quite a few of us out there diagnosed and Im afraid alot more may get it if they dont take Celiac and the diet serious.
Please remember now that you know look ahead and take care of yourself. My daughter hasn't slowed down much at all (then again) we didn't know anything was the matter with her. I had never even heared about Celiac till July 2003 and all those little signs came together. the only sign of sickness that I see now is she is still small, pale skin, and gets tired by the time the week-end rolls around. Between playing soccer and running up to two miles a day Im tired just keeping up with her..........
Hope this helps,