Have you had any GI tests done or any GI specific blood tests to check for things like Celiac Disease?
They're probably referring to Ulcerative Colitis, but wouldn't be able to give you a specific diagnosis without doing some tests like endoscopy, colonoscopy, etc.
I have Celiac Disease and my main symptoms were painful bowel movements,
frequent diarrhea that over the years got progressively worse, and then finally right after I was diagnosed they determined I was anemic due to malabsorbtion issues from having the Celiac Disease go undiagnosed for over 10 years. (How's that for a run on sentence, lol

) I also was always overweight and I know a lot of Dr's assume you have to be underweight to have Celiac Disease which is
not true.
Good luck!