A related discussion,
Green stool was started.
I'd definitely take him to see the doctor, but, and I mean but, some pills cause green stool, chlorophyll or diets of salad, only salad and greens will defintely cause a green stool, I've had them and they go away, and it's usually when i take chlorophyll tablets or when i eat salads, they go away when i go back to my meat diet. I'd ask a pharmacist for side effects to some of the pills he's talking and he will probably tell u that there maybe green stool involved with certain pills.
I've read comments on this board or maybe where people had this same thing. About a month or two ago. Keep looking down at the older postings.
Get a liver enzyme test, ASAP. It sounds like the antibiotics are affecting his liver. If this is the case, it's best to catch it early.
if it's not a result of something he ate, bile colored stool (dark green/black) usually means that his transit time (how quickly things are moving thru him) is a bit too fast for his body to be able to reabsorb the bile. if he has a stomach bug, that could very well be the reason. since he is running a fever, he should go to the doc. with a gi bug, as mom's can atest, it's good to stick with a BRAT diet (bananas, rice, applesauce and toast) to slow things down. lots of non-caffeinated liquids, too.