I have similar circumstances. Even a drink of water can end with a belch. I have eaten a bland diet my entire life.
All my GI tests have been inconclusive over the years too. I think there may be a genetic connection as my father had and my daughter has similar digestive issues. Like an extreme sensitivity that our GI systems didn't develop normally following birth. Idiopathic IBS is another diagnosis that I have been given. I just had an elective colon resection this week due to mild diverticulitis. Maybe this will help. Who knows?