Unexplained gas

Allergic reaction? My feet get red & hot, my hands get red & hot & sweat. My abdomen swells, visibly swells... rapidly. Sometimes on an empty stomach... sometimes after eating, sometimes after a glass of water... resulting in a violent burp similar to a dry heave... I call it screaming like a banchi... no food comes up just gas... I can be herd through solid walls. The biggest pressure point is at the centerline of my lower rib cage. Been scoped, blood test nothing found... what can it be?