Thanks for your query.
as you said your son is sick for about 2 weeks initially having respiratory infection and now having gastrointestinal infection
.i advise you to consult your pediatrician
In the meantime try to maintain hydration,give oral rehydration fluid sip by sip.give coconut water.also give him some antiemetic in prescribed dosage.look for his urine output.his level of consciousnes.In case you find him dehydrated take to ER,
Your son will be fine.