Hello and welcome I really appreciate your concern for your son. Looking at your description it seems to be related to dehydration owing to working in hot and humid environment. another possibility is chemical injury to the throat and pharynx which also can cause vomiting I would advise you to give him plenty of fluids including ORS, fruit juices and plain water mixed with salt and sugar to counter dehydration and electrolyte imbalances. you can give him antiemetic drug like domperidone or ondansatron group of drugs. Antiacidity medicines like pantoprazole or ranitidine with antacids with definitely help him Hope I could answer your question, please feel free to ask for further clarification. Best wishes