Hello! I have been through your question. Related your concern I think this could be an bacterial gastroenteritis more possible shigellosis, but to be sure to say this your son has to do stool culture , full blood count (as he has done ), azotemia/creatinemia (to see renal function), electrolytes, abdominal echo and meet an infectious diseases specialist to do a differential diagnosis and start antibiotic ( usually I prescribe ciprofloxacin). During this time what I suggest for him is to drink a lot of water, tea with tresol, take probiotics, eat toast bread, cheese, yogurt,boiled eggs, banana, and should avoid milk, meat, fast foods, sparkling drinks. I hope my answer helps you. I wish your son a quick recovery.