Babies are born with some immunity to infection which lasts about 3 months. After this they may suffer from sicknesses such as colds and sick tummies.
Fortunately, most illnesses are mild and clear up without treatment, but, at the time, it can be very worrying for new parents.
Knowing what to do when your baby is ill and when you should call the doctor is something that comes with experience.
You are the best person to judge whether your baby is unwell, as you know your baby better than anyone else. If you are unsure always seek medical advice.