How come only allegra (fexofenadine) is effective with my food allergies, but no other product works? i don't have indoor/outdoor or seasonal allergies. only food.

Everyone's different: Many people prefer one product over another. It also depends on what symptoms you're trying to treat, and whether they are truly allergy or ige mediated. Antihistamines will frequently be ineffective in gastrointestinal symptoms. Generally food allergies are treated with avoidance. If your food allergy diagnosis and treatment are unclear, an oral challenge is really the only way to diagnose.