Fever can be a sign of dehydration.  But not feeding can be a sign of
a sick baby.  And with fever, it is more likely that the baby has some
sort of infection which is making him refuse the breast than the baby
is dehydrated and therefore has fever.

I would want this child evaluated quickly.  Maybe it's nothing, but
not feeding, especially when the child is sick is not a good sign.
When breastfed babies are sick, they often feed more, not less, unless
they have sores in their mouths.

Jack Newman, MD, FRCPC