As you have found gut problems are extremely complicated and most docs have no clue, it seems. Here are some basics to check which you may have not done:
-- find out if you have SIBO(small intestine bacterial overgrowth). It has many causes but the most common is bacteria normally residing in the Colon migrates upward into the small intestine. These bacteria react with carbs and other things to cause both hydrogen and methane gas, mostly. These can be sensed. Search on "aerodiagnostics" and buy a test and take this to your MOST trusted doc or better yet an Integrated medicine doc.
-- on line solutions are possible too: Search "digestivehealthinstitute.org"
AND "sibo.info" "sibo.sos"
The on line stuff will educate you and none of this is simple to understand or INexpensive. You must steal yourself for the battle ahead.
There IS hope. Do not give up.

Good luck kiddo.