Hello, 
He needs to be physically examined by a GP & get blood & Imaging tests done. 
Such symptoms commonly occur due to food 
poisoning, developing typhoid infection, liver disorder, 
indigestion, 
dehydration, lack of nutrients in his diet.
He should take ORS, soups & juice to help maintain the electrolyte balance of the body. 
He can take 
Loperamide & Imodium to control diarrhea. Let him take homemade boiled food, avoid spicy greasy food & addictions if any.
He should visit ER, get physically examined, get Liver function & other tests done. Take 
Acetaminophen (Tylenol), one sos when backache.
Hope I have answered your query. Let me know if I can assist you further.
Take care
Regards,
Dr Nupur K, General & Family Physician