Welcome to HCM!
From your question I can say that your son has an infection ( gastric- intestinal ) and should be started on a good , broad spectrum antibiotics, as nausea,
vomiting and
diarrhoea, all point towards the possibility of an infection.
It will be good to start with an injectable antibiotics, may be
cephalosporin, as he can't eat right now, and injectables work faster.
For his nausea and vomiting, I feel that
perinorm injection are good in stopping this.
There is a possibility of food
poisoning, but one needs more information. however, the medicine almost remain remains the same as mentioned above.
Please do not panic, getting routine blood tests, vitals measured- like ...blood pressure, sugar levels, and an USG abdomen will make the picture clearer.
blood counts will help in finding the cause of infection. It is a common presentation in case of a strong abdominal infection, which is completely curable.
With proper medicine, I can assure you that he will get better in few days.
Hope your son get well soon!
feel free to ask more questions
Dr, Manisha gopal