this happens to me all the time because (although i have an above average immune system) my tonsels are shot to shit and they get infected 3-4 times per year (yes, i know i should remove them, but the doctors won't put it on my insurance unless i go through severe pain... I don't want to talk about. it's one of the reasons i hate doctors)... so i go on antibiotics pretty often and i experience this a lot.
stay away from starchy and refined carbs for a week... keep your carbs sources limited to fruits, white rice (this is the exception), and veggies. take in lots of psyllium husk (metamucil) (2-4 servings per day), and take some acidophillis (hope i spelled that right) for around a week.
and don't forget to drink lots of water. It usually takes 5-7 to stop the abdominal discomfort and your gas from smelling like someone opened a manhole.