Gases produced in the large intestines (colon) usually travel toward the anus. The ileo-cecal valve, pyloric sphincter and cardial sphincter together with the intestinal peristaltic usually don't allow those gases to pass in an opposite direction. In your case, the gases seem to be traveling toward the mouth and disorders of the sphincters (mentioned above) and intestinal peristaltic create this scenario. This is one of the symptoms of irritable bowel syndrome (IBS).