I'm sorry, I really disagree with your Ped.
I would NOT let a 6 week old, cry it out. At all. Their brain/nervous system is not even fully developed yet. They ALSO have an instinctual 'startle reflex" which they CANNOT control... and this wakes them too.
AND they need to feed on-demand.... and per their growth-spurts and per their 'cluster feeding'.... which is 24/7, day and night. For the 1st year of life.
Each baby is different... and for me, I go by my child's cues.... and needs....
My daughter, my firstborn, was REAL difficult... to put to nap or bed.
My son, my 2nd born, was real easy and still is.
For both, I went by their cues and needs and feedings, on-demand.
BUT despite that... as they have grown and matured and gotten older... they are SUPER good sleepers. Naturally.
Sleep... is never finite nor static in a baby. And, per age-stages and phases... a child will ebb and flow, per sleep or naps. Older children, Pre-teens, Teens, College kids, Adults, Elderly... ALL have differing sleep patterns or difficulties... and no person I know has slept the same way, they did as a baby, nor gone to bed at the same time since they were a baby. It changes.... per age.... and age-related development....
Go by HIS cues.... a newborn typically naps a lot. They get "tired" after about only 2 hours of awake time....