Occasional smelly gas may be from foods containing sulfur, like: poultry, meat, eggs, dairy, nuts, coconut, legumes, tea, coffee and certain vegetables, such as tomatoes, cabbage, asparagus, broccoli, onions, garlic, and fruits, such as avocado, banana, watermelon.
Fructose malabsorption is commonly misdiagnosed as IBS. In this condition you get loose stools after eating foods, high in fructose or sugar alcohols (sorbitol, mannitol...), so after fruits or anything sweetened with fructose, HFCS, table sugar (fructose + glucose), or sugar alcohols (polyols).
I seriously doubt probiotics will help you. Probiotics, as I know, help only in bacterial diarrhea and Clostridium difficile overgrowth caused by antibiotic therapy.