You have not mentioned the frequency or consistency of loose stools.
Bile secreted in small intestine
if rapidly passes through rest of the large intestine as happens in diarrhea
-due to increased movement of the intestines- the stools will be green in colour.
If there is no blood in stools/ no high grade fever/ no abdominal pain- its likely to be viral. In such a case, antibiotics will not be needed.
Be sure he drinks and eats well. Give him plenty of curds, water, ORS, vegetable soups, rice based food etc. Avoid fruit juices.
Be sure he passes urine atleast 4 to 5 times a day.
You may give probiotic
sachets like Econorm/ Bifilac
In case he does not drink well/ his urine output is low/ he is tired/ has high grade fever/ you see blood in stools- you might have to visit your Pediatrician
Hope my answer helps you.
Wish your son a speedy recovery.