Just something to keep in mind if the doctor's don't find an answer on the normal battery of tests. I have a condition called gastroparisis which was caused by long term use of narcotics. Basically, narcotics slow down the motility of your stomach, in my case, they shut my stomach down completely, and after I would eat, the food would sit in my stomach and rot. For several months, I had the exact symptoms you are dealing with now, but eventually I started vomitting and could not stop, and nobody could figure out why for almost a year.
Finally, a new doctor I had called in, did an easy test called a "stomach emptying scan" where they have you eat some food that has a radioactive dye in it and then they take pictures of your stomach every 15 minutes for 3 1/2 hours to see how long it takes for your stomach to digest the food.
I have a device called a gastric stimulator (it is actually the same exact device as the Spinal Cord Stimulator, but it is implanted in my stomach), and it stimulates my stomach to work, and it has cut my symptoms by about 85%.
Just keep it tucked in the back of your mind as a possibility, if they can't find the culprit easily.
If you have any questions, feel free to ask.