Hello,
Since he is nauseous & is vomiting you can give an antiemetic (
Pepto-Bismol) but if he vomits that out, let him get an antiemetic (
metoclopramide) injection to stop vomiting. 
After that let him take ORS, soups without spice, oil or butter, juices to help balance Na-K in body & that will also make up for the 
dehydration & weakness that he is experiencing. You can give him semi-solid food in small amounts 4-5 times.
For bodyache give 
acetaminophen (Tylenol) one sos when required. Let him get physically examined in ER to rule out any enlargement in the liver. Let him have blood workouts done (CBC, Liver function tests, 
Urinalysis, USG if required). Further treatment will depend upon the evaluation & the degree of his illness. 
Hope I have answered your query. Let me know if I can assist you further. 
Regards,
Dr. Nupur K, 
General & Family Physician