Hi, Welcome to health care magic, Severe left side stomach pain with fever and black stool could have many causes which are acute gastritis or diverticulitis or food allergy or food poisoning. In your case it is likely because of gastritis or diverticulitis. Your should undergo routine blood investigations and serum electrolytes ,liver function tests,urinalysis and stool for blood and abdominal ultrasound to detect the underlying cause. Treatment is mainly symptomatic if there is no infection. Although antibiotics like norfloxacin with tinnidazole should be given for at least 3 days small course with anti-emetics like tab.ondasetron mg twice daily. Antacids like h2 blockers (ranitidine) or proton pump inhibitors (pantoprazole or rabeprazole) will help to reduce excess acid production in stomach. One can also take digene gel or liquid or ulcero-protective agents like sucralfate or bismuth subsallicylate to reduce the burning sensation. Apart from medications he should eat plain foods like boiled rice and green leafy vegetables without adding spices or oil.avoid oily,spicy and fast food. Consult physician or gastroenterologist for detailed medical history and clinical examination to diagnose the cause. Thanks and Regards,