I am a 62 year old male who eats very healthy but am experiencing abdominal pain and nausea after eating most meals. (pain is in my central upper abdomen) This has severely reduced my appetite over the past 1-2 years and has caused me to loose almost 20 pounds of body weight ( 6 feet tall, currently 155 pounds). No problem with constipation or diarrhea. An endoscopy, endoscopy, abdominal ultrasound, abdominal CT Scan, and HIDA scan have all been negative. What is the cause of my abdominal pain and loss of apetite?