I have a 3 week old son, who I've been breastfeeding exclusively I've had to go back to work sooner than expected and so I've had to supplement with formula 2 oz formula 1 ounce breast milk. now he's having a hard time pooping. and when he does poop with the help of Vaseline it's not hard, so he's not constipated. what do I do? he goes 24 hours with out pooping and he's so miserable.