It is common for babies to be sick, often in the early weeks as they get used to feeding and their bodies develop. Possetting is bringing up small amounts of milk, when your baby vomits this will be a much larger amount. It can be frightening for your baby, so they are likely to cry. Lots of things can cause your baby to be sick.
Make sure your baby is positioned correctly when breast or bottle feeding as incorrect positioning can cause a baby to be sick.
Being sick often or lots of it, may be due to ‘gastric reflux’ where acid from the tummy can come up again. Babies can be grumpy and it can sometimes lead to poor feeding. If your baby is feeding well but doesn't seem themselves, you may just need to change the baby's position during a feed to make them more upright. Feeding smaller amounts and more often may also help.