I have good days and bad days, somewhat related to how late I stay up compared to when my son gets to sleep for the night. Today I took a walk with the dog and the baby, and could not believe how exhausted I was! The walk helps my dog and puts C to sleep in the carrier, but I don't know if I can regularly do it yet, because I'm just sooooo physically tired, my legs feel like lead. I got a nap today and that helps. Monday we went back to bed after our morning routine (nurse, some awake time, bath) and slept an extra couple hours :) He doesn't sleep well during the day, so "sleep when the baby sleeps" doesn't really work for me.
Countrymouse - I use prefolds/covers during the day, but switch to pockets at night with the larger insert because he sleeps better - I think the diaper doesn't feel as wet as prefolds feel, so he'll sleep through wet/dirty diapers. Probably gross, but I only usually change him once in the night (sometimes twice), and we're all ok with that :)
B vitamins sound like a good idea. I still take my prenatal but I dropped my iron supplement at week 3 PP, that might be part of my fatigue.