What Causes Loose Stools And Vomiting While On Treatment For Bacterial Fever?

My elder brother aged 25 is having bacterial fever for the last 4-5 days. He took antibiotic as per prescription. After few days he got loose motion. And 2-3 days back he got temperature every night. Now from yesterday he is having vomiting after whatever he eats. Kindly suggest something. He can't eat anything.