Re: stretching time between feedings?
your pediatrician sounds like he doesn't knowm uch about breastfeeding. stretching out feedings like this can absolutely hurt your supply, and there's no guarantees at all that it'll result in longer stretches at night. in fact, my guess is it will result in MORE nursing at night to make up for the missed feedings during the day. which some moms are ok with - "reverse cycling" is something especially working moms sometimes like, especially if they're cosleeping so that all the extra night nursing isn't very disruptive.
my suggestion - just don't watch the clock. not now, not really ever except to nurse MORE often. feedings naturally space out when the baby is physiologically ready for it, often gradually throughout the first year and a bit more once they're taking in reasonable amounts of solids (sometime between 6-12 months for most). you might also try switch nursing - puttin baby on both sides, or even 3-4 sides, and doing manual compressions while baby nurses, to try to increase the amount baby takes. but your 6 week old's feeding patterns are COMPLETELY NORMAL (even though your pedi seems to be implying they're not).
eta: unlike with formula, breastfed babies don't really increase the amount of milk they take in, from about this age till 6 months (when it gradually declines due to replacement with solid food, though nursing should always be primary food till 12 months). perhaps your pedi doesn't remember/know this.
hang in there!
Nursing, pumping, cloth-diapering, babywearing, working professor mama with the awesomest SAHD ever.