how my son gets weight any drops for health grow he is full active only weight low

A. Hai good morning !! Babies increase 400-800 gm per month,by 5-6 months they double their birth weight. Check if baby gaining average weight of 500-600 gm per month. Until 5 complete months exclusive breast or formula milk is suggested and vitaminD3 drops as supplement of vitamin D rest all nutrients,minerals will get from breast milk so give breast feed every 2 hours.