Hi. Thanks for your query. Noted the history about your patient and understood the concerns. Since the patient is taking a lots of antibiotic for bronchitis it is possible that the gastrointestinal bacterial flora has changed to the extent of changing the color of stool to green indicating super-infection with opportunistic bacteria. This can be diagnosed by the following Get the stool tested for three consecutive days. Get blood sugar, CBC and other relevant tests. Ultrasound of the abdomen.Clinical evaluation in general and of abdomen. Once diagnosed give a proper treatment as pr the findings and cause found out. Probiotics, activated charcoal and multivitamins should helps as also increase in yogurt/curds and banana also help. If these things do not help the patient may need an antibiotic active against intestinal infection and metronidazole. Give soft and bland diet.