The pediatrician told me that i should keep my 18 days old son without feeding from 12 am till 6 am even if he cried all night. is it true?

Unusual: This recommendation is unusual. General feeding recommendations are to feed the infant every 2-3 hours. You can feed every 2 hours during the day, and stretch to every 3 hours at night. This is especially important if you are breast feeding. Babies typically can sleep through the night much later( 4 months and older). I suggest you talk to your pediatrician again and clarify this recommendation.

Feed the infant : I am a proponent of feeding your 18 day old every 3-4 hours, so feeding during the night is appropriate. This will improve a bit over the next few months, but brain growth is extraordinary during these early days of life and feeding at more regular time periods is best! congrats on your new baby. The first year of life is exceptionally rewarding and recommend lots of pictures and videos!

Not quite yet: Put your son on his back in his own crib to fall asleep. The 1st 6 weeks what he needs & what he wants are the same thing. Make sure he's awake before you night feed, not just crying out in light sleep.If you put him to bed drowsy, but awake at a consistent time, sleep consolidation can occur between 1-4 mos. Read, rock & wipe out his mouth after the last feed to set good habits by 4-5 mos.