What Causes Abdominal Pain, Nausea And Loss Of Weight?

Hi there, I have been having abdominal pain, feeling nausea and vomiting mostly after meals for the past 4 months. I have lost 8 kg since having those symptoms. I have gone for a GI upper scope, colonoscopy, capsule scope, ultrasound and CT scan of the abdomen and it all came back negative. My specialist is perplexed and have prescribed all types of medicine possible and on anti-depression to relieve the pain as well as Bascupan alone does not seem to be working. He has ruled out being depressed as there are no reason for me have that and any related diabetes related GI problems have asked to seek a second opinion. Not wanting to go through all the test again, are there any specific thing that I should look out for? I am a 32 year old diabetic female and have been diagnosed with gastritis to acute gastritis and now chronic gastritis by the specialist.