I agree with @kinetic14 it works...had to do this for my baby girl and she usually went within seconds...it helps to stimulate the mussels they use to go poop and when they are that young they are still learning to use them. it's not good to give a baby that young juice or water.

or literally a ounce of diluted apple juice

I know it sounds weird, but put some vasaline on a qtip and gently insert it into his bum and swirl it for a few seconds. trust me, it works.