A 2-day-old male neonate born to a 28-year-old primigravida 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 delivery. On examination, the baby has tachypnea (respiratory rate 65/min), mild hepatomegaly, and poor perfusion with capillary refill time >3 seconds. Blood culture is pending. CBC shows WBC 3,200/μL with 85% neutrophils and 12% bands. CRP is 18 mg/L. What is the most appropriate next step in management?