Most likely your son is suffering from
gastroenteritis also known as
stomach flu.It is an intestinal infection marked by diarrhoea, cramps, nausea, vomiting.However its not necessary that all symptoms are present in every patient.Mostly Bacterial,Protozoal and viral infection causes inflammation in your stomach and intestines causing symptoms like vomiting, severe abdominal cramps, and diarrhea.You should get a stool routine and microscopy test done to see the cause of infection.If possible
ultra sound abdomen should be done.
Treatment to be discussed with your treating doctor-
Take imodium 2mg stat.
Zofran 4mg(ondensetron) can be taken for nausea along with Neksium 20mg(PPI) to provide symptomatic relief.
If
stool test is positive for bacterial infection,Therapy with Antibiotic like Cefixime and anti protozoal like
metronidazole can be given for 3 days.
Take a lot of soluble fiber in diet.
An over counter probiotic should be taken thrice a day.
Drink a lot of orange juice and coconut water.Take juices rich in potassium to compensate for electrolyte loss in stools.
Keep yourself hydrated,Drink plenty of boiled water.
Eat light food,Avoid spicy and junk food.