S.H.
for the 1st year of life... Breastmilk or Formula, is their PRIMARY source of nutrition... NOT solids, and NOT other liquids. And certainly NOT juice.
Even water if not recommended until about 6 months. They don't need it. They are getting nutrition from breastmilk or Formula.
Bear in mind, that every 3 months is a "growth-spurt" in a baby... and you NEED to feed ON-demand... formula or breastmilk. They need it, 24/7, day and night.
Your baby is ONLLY 4 months old... their digestive system is still developing. You cannot just give him things...
Ask your Pediatrician. You need to do that.
You can't just give a 4 month old things, willy-nilly.