Why Have I Completely Lost My Appetite And Gag Everytime

why have I completely lost my appetite and gag everytime I see food? I have lost 20 pounds in six months. I have a cough too along with heartburn. My dr did a endescopy procedure and a colonoscopy which turned out pretty normal and a c t scan which turned out normal. Why can't they figure out what is making me gag on everything I try to eat?