Nothing that young. Bicycle his legs, a warm bath, the I love you belly rub.. they’re just getting used to eating so pooping is a whole body experience.
Chances are he’s just straining to go. The older he gets he’ll learn to loosen up and go.
Call his pediatrician before giving him juice. If they say it's ok to give baby they will want it mixed in with something else most likely.
Lots and lots of fiber, water, prune juice