hi my baby boy is 4 days old . my baby is taking milk only from left nipple as my right nipple is very small. how can I make my baby drink from both the nipple.

Do keep trying to latch baby on the other side. You can start with the breast which the baby prefers and then once the baby is sated you can try the other side. In the mean while you should do some gentle nipple massages to help prepare the nipple and it is easier for the baby to latch.