Hi Till 6 months of age Exclusive Breast Feeding is the best for your baby. If you are on a nutritious diet and adequate rest, there is no reason for reduced milk output. Your diet should include plenty of fruits, vegetables, nuts, milk, egg etc along with routine things you eat. You must be sure that you get extra protein and calories so that you will be able to produce adequate milk. Due to numerous reasons Exclusive Breast feeding is the best for your baby and you too. If his weight gain is adequate, there is no need to supplement him with formula. Zerolac is a lactose free formula and is given in infants who are having loose stools due to lactose intolerance. And some infants with viral diarrhea develop temporary Lactose intolerance and will not tolerate normal formula. So your doctor would have suggested this. If your baby is completely out of loose stools now, you can stop Zerolac. Continue to breastfeed him. If your breastmilk is really insufficient (Baby is losing weight or not gaining weight) then you might opt for normal formula like Nan 1/ Lactogen 1. Zerolac should not be given routinely unless your baby is proven to have Lactose Intolerance. When ever you give formula- please give it with spoon and try to avoid bottle. Bottle feeding will be much easy for your baby- he will develop nipple confusion- and eventually stop feeding on your breast as it will be a difficult job for him. Hope my answer helps you. Before ending I wish to stress the fact that Exclusive Breast Feeding is the best for your baby till 6 months of age. Best wishes.