A 4-year-old boy from rural India presents with a 3-day history of severe left ear pain, fever (39.2°C), and irritability. His mother reports he had an upper respiratory tract infection 1 week ago. On examination, the left tympanum is markedly bulged, erythematous, and under tension. Otoscopy shows loss of normal landmarks. Audiometry is deferred due to age. What is the most appropriate immediate management?