Most babies bring up milk after their feed; usually it is just a little amount but it does sometime look like most of the feed. Many mothers will complain that their baby is vomiting all the milk; yet one finds that the baby is gaining weight as he should. He must therefore be retaining enough of his feed to let him grow so well.
Bringing up milk after a feed does not mean that the milk does not agree with the baby. Babies just normally do so, though some babies are certainly worse than others. If your baby tends to vomit be especially careful to hold him up for some time after his feed so that he can bring up any air that he has swallowed in the process of taking his feed and allow the milk to settle.
In babies the upper end of the stomach does not close as efficiently as in adults. Hence there is a chance of the milk spilling out while the baby is laid down. It is therefore safer to lay him on his side so that any milk he may bring up will spill harmlessly on his bed and will not choke him. Some babies will still vomit large quantities of milk after most feeds specially the babies who are tense and irritable. And medicines may have to be given to help these babies.
If the vomiting is really troublesome and your baby is not gaining as much weight as he or she should you must visit a doctor as your child may be suffering from a problem known as pyloric stenosis and the only cure for that is surgery and it will have to be done immediately. This condition is much more common in boys though it is possible that a girl can also get it. This condition is noticeable when the baby vomits out all of the feed and gains very little weight. It is not a serious surgery and the problem of vomiting will be cured soon after and the baby will begin to feed normally. Check on the amount and frequency of vomiting before you start to worry.