Mama, please don't buy anything without a doctor's go-ahead, kahit walang reseta, lalo na para sa baby, okay? Your pedia should really suggest something specific for underweight, and if hindi ka satisfied, you deserve better care. Honestly, marami sa amin nag-seek ng second opinion kahit tight ang budget, try mong hanapin ng pedia na may free or lower consultation, o mag-inquire sa health center near you (mas mura often). Before trying anything, you really need guidance kung ano talaga ang root cause ng weight issue niya, could be feeding, absorption, or something else, at depende yan sa proper assessment. Mag-push ka talaga for a better answer from a doctor, mama. Your baby's health is too important to guess on.