Many babies bring up milk during or shortly after feeding: this is known as regurgitation, reflux or sometimes as posseting. It is very common in young babies, and normally passes by the time your baby is a year old. Reflux doesn't usually require treatment if your baby is putting on weight and seems otherwise well.
Much more information about reflux can be found on the NHS Choices website, including information on treating reflux, but their summary of the main symptoms, causes and tips is:
Signs that your baby may have reflux include:
spitting up milk during or after feeds – this may happen several times a day
feeding difficulties – such as refusing feeds, gagging or choking
persistent hiccups or coughing
excessive crying, or crying while feeding
frequent ear infections