It could be Various reasons, may be baby is colic, may be bottle is not clean & sterilize properly. Plz consult to your doctor.

Newborn babies have weak immune systems. Only Breast feed provides the newborn baby with antibodies to help fight infection. As a result, breastfed infants have fewer infections than babies who are bottle fed.<br> Make sure you take in plenty of water, sports drinks, or other clear liquids. Take small sips. Infants should get plenty of breast milk, and toddlers can drink electrolyte solutions such as Pedialyte.

There are many reasons at this age, you need to keep baby clean his hands should be clean

It could be anything .. anything contaminated... How old is the baby??