i have the same problem. i limit my intake of foods i am allergic to (wheat, dairy, and corn, which are quite common allergies) and also any preservatives and msg ...both of which are in darn near everything, so i read labels carefully. also, i daily take an acidophilus and probiotic complex. i stay away from other irritants like sugar, alcohol and caffeine.
just taking those life changing steps have made a world of difference! good luck, i know it ain't a fun ailment