I have had very foul smelling gas which seems to respond to probiotics. once i stopped taking probiotics (after a few weeks), the problem came back. ?

Combination: Gas odor is a product of combinations of food, consumed, digestion, and bacteria in the intestine which aid digestion. From your response, a large factor for you is the intestinal bacteria. It frequently takes months of supplementation to change the flora(bacteria makeup) of the gut. Keep up supplementing, eat healthy, and avoid antibiotics.