I would push for a capsule endoscopy. It will show what is going on in the are that endoscopy and colonoscopy don't reach. I agree with jamosca, lay of the soda and fried foods. Try a meal replacement shake. I make them using a non-dairy milk, almond butter and frozen fruit. My meal replacement powder of choice is Raw Meal because it's vegan and sugar free. You can also try soups and juicing. The liquids are easier on you system but can still get you the calories you need. Perhaps the doctor can give you an appetite stimulator. Maybe try another GI. I went through more than I can count over the course of 20 years until I was finally diagnosed with Crohns.
Crohns, Psoriatic arthritis, Psoriasis in my nails, Hashimotos. Meds- Synthroid, Remicade, Methotrexate, Vitamin D, Biotin