I want him to get back in his original weight and like what he was earlier like a very happy baby he is getting little bit tired these days

A. dear Mum, your baby seems to be only 4 months old. so, you should exclusively breastfeed till 6 months complete. that's the most healthy way to gain weight. At one episode of breast feeding, feed from only one breast so that baby receives fat rich hindmilk which will help in weight gain.