Hi, Welcome to HCM. Nausea, diarrhea or stomach cramps could be due to gastritis or gastroenteritis or food poisoning etc. Eating spinach might cause slightly greenish stools but as you said you had a whole green coloured stool and then it turned back to yellow. it can occur in various conditions like excess unprocessed bile (which is to be digested by certain enzymes)or iron supplements,or iron riched diet,celiac disease or Protozoa infestation etc You must go for routine blood tests,urine and stool tests and serum electrolytes mainly sodium,potassium and abdominal ultrasound. You must be treated with antibiotics and antispasmodics,anti-emetics with water and electrolyte balance to avoid abdominal cramps. Consult some nearby physician or visit ER for complete treatment. Regards, You must take him to the gastro physician considering him as a adult as far as treatment is concern. Thanks