IT IS NOT DEHYDRATION!!! It is normal!!!
Especially in boys. I'm amazed her ped didn't totally reassure her. Oxalate crystals in a newborn's urine is a transistion to extrauterine life/food thing, and although usually occurs around day 4-5 and doesn't last more than a couple of days, it is normal! If he has 6-8 wet diapers a day, he cannot be dehydrated, and some babies are just sleepy! How's his weight gain?
I can't say strongly enough that this by itself is NOT a reason to supplement.
Barbara, LM, CPM and who has seen a lot of this, including my own son.