Baby’s weight gain

Hello mamas, My baby is 5 months old and his weight is only 5.5kg. He’s always been 3rd percentile or below since birth. He was initially breastfed , but due to lack of supply now mostly on formula. Initially I gave Lactogen and then started giving FairPrice Gold ( as it claims more probiotics)formula two months back. I’m bit worried if his weight will never improve. Doctors at KKH and polyclinic doesn’t give any recommendations for formula. They always check and say it’s Low. Last time, PD suggested I can try weaning at 5 months. So I only started giving rice cereal (1tbsp) per day for around 4 days now. If anyone in my situation, could pls share any tips for baby’s weight gain either formula or from weaning. #firsttimemom #infantformula #babyweight #weaning