Being aware like MadB so fantastically described is very true. All babies grow at different rates, and all have super cranky days periodically (Don't we all though? )
My DD2 was born close-ish to your DS3. DD2 was born at 40w5d on 1/11/13, and although she's my third, i've noticed she (like her siblings) isn't the typical baby depicted from the MCHN booklet, and that's cool with me and them, she's thriving regardless and at her own natural rate. I refer to them as a guide, when I feel I need/want too