My 15 Year Old Grandson Woke Up This Morning With

My 15 year old grandson woke up this morning with severe stomach pain, vomiting and mild diarrhea. He has continue to vomit throughout the day and is to the point of just throwing up greenish bile. Tried some 7-Up a couple times but didn't stay down. The stomach pains have brought him to the point of tears. Is this just the 24-hour flu bug or something more severe?