A baby’s fever after diarrhea may be due to decreased immunity caused by gastroenteritis, leading to the recurrence of fever symptoms. Persistent fever can trigger seizures, so it’s important to seek medical attention early to prevent serious complications. It is recommended to undergo a chest X-ray to check for lung inflammation, use antipyretic medication to reduce fever, and consider using azithromycin for treatment. Additionally, drinking syrup is advised to clear the lungs.