Constant with or without food upper abdominal pain, diarrhea, constant burp like sound from upper abdomen, only test that shows is low b12 and mch/mch?

Need more info: This format doesn't lend itself to making adequate guesses of what is going on. That said, i think about reflux, ulcers, gastritis.

Low b12: Low B12 indicates either low B12 intake from foods (meats, dairy) OR malabsorption of B12 at small intestine. Malabsorption of B12 can occur from small bowel disease or from stomach disease, with lack of intrinsic factor production at the stomach. Low MCH indicates low hemoglobin per RBC corpuscle, so your B12 deficiency is causing problems. Get GI workup and B12 absorption work up.