What Causes Dark Coloured Stools Along With Vomiting In A Child?

Hi sir, i just want to ask, my son right now is taking a medicine metrodinazole, he is diagnose of amoeba, i was so worried because earlier this morning, his stool is still loose but no foul smell, but my husband sees some dark color in my son stool, and he vomited this afternoon with no reason. thank you