According to me you are suffering from gastroparesis, meaning no cause is known after going for test also but still according to me you are suffering from kind of gastrointestinal disease. My opinion is to you to start with bland, low-fat, low-fiber diet, you will feel better.
Next Steps
It's better to meet and Consult a near by dietician to get proper diet plan or you can contact me through mail drdotmedidietatgmaildotcom here dot means . and at means@