Hello there, It is important to know the weight and height of your child. If your child weighs less than 10 kg and has a height less than 80 cms, he needs a proper evaluation. It is equally important to ensure if breast milk has been adequate and also if the technique of breast feeding is correct. Incorrect breast feeding technique results in an undernourished child. It is possible that your child s immunity may be low and this can be the main reason. However recurrent infections of the respiratory system and skin require further evaluation. Zerolac is prescribed if there is lactose intolerance. This can be tested with a stool test for reducing sugars and clinical signs like excoriation of skin around the anus. You can introduce eggs, bread with butter, cereals and lean meat which are all energy dense foods. Take care.