A 3-day-old male neonate born to a 28-year-old primigravida mother presents with poor feeding, lethargy, and temperature instability (rectal temperature 36.2°C). The mother had prolonged rupture of membranes (PROM) for 18 hours before vaginal delivery. On examination, the baby is hypotonic with weak cry. Blood culture is pending. CBC shows WBC 22,000/μL with left shift (immature:total neutrophil ratio 0.4). CRP is elevated at 8 mg/dL. Blood glucose is 45 mg/dL. What is the most appropriate immediate management?