im thinking either IBD or celiac disease
I would encourage you to see a gastroenterologist and also familiarize yourself with a disorder called gastropheresis. Follow up on the results of your test. If you are not eating a lot, you aren't going to make a lot of poop.try to eat something if even a cracker, you don't want to get into electrolyte problems and malabsorption issues either . A ct won't show this disorder and not all docs are well educated about it. As scary as what you are going thru is, chances are you are tumor free.they need to do other tests to check for an ulcer.feel better soon!
Have you seen a gastroenterologist about this? Have you had any other testing done? A CT would usually show a tumor if you had one, but it won't always show an ulcer.