Hello,I have gone through your question and understand your concern. Let me give you a brief explanation on the topic of growth in children, to help you get a clear idea about growth in children. To start with you must be aware growth in children is measured by using growth charts, from the time your baby is born your doctor will note her length, head circumference and weight. Each time you visit your doctor for vaccination or other general check up, your baby will be measured and tracked over time. This is plotted as a growth chart and checked that your baby is within the normal range [WHO standards]. From your question I assume that your baby girl falls in normal weight range, with her age & weight considered by me as 3 months & 5.4 kg her weight according to WHO standards should fall within the range of 4.6 to 7.4 kg. Lastly, mother’s milk is the best source of nutrition. For first six months, exclusive breast feeding is enough for the baby to maintain a normal and healthy growth. I personally discourage the use of milk substitute for babies below 6 months within normal growth range, my advice to you is to increase the frequency of breastfeeding to increase your babies weight. Hope your question is answered. Thank you.