I was a bit upset when I realised we have only two photo's of me while I was visibly pregnant, one at six months, so a smallish bump, and one at 38 weeks with a bloody enormous one. It's not the best photo either and I'd got it into my head that somewhere there ought to be at least one lovely one of me, looking all round and glowing in glamorous maternity wear and lovingly holding my belly, so I could show DS it in years to come and he might want to put it in a nice frame. I blame that Christmas film Sarah Jessica Parker did for that, I watched it in the grip of hormones and it gave me ideas. 
What we actually have is one picture of me in stretchy sweatpants and a hoodie that wouldn't zip up across my belly any more, looking like death in need of a good bath, hauling my bulk across the living room in search of the Gaviscon and seething with 'end of pregnancy rage'. Nobody's framing that one.
But for a good few weeks after I realised I'm missed my photo opportunity I felt quite sad about it.
I know you can't go back and take the photo's but they aren't the only way for you to remember the newborn days.
Can you write down anything and everything you remember, so you can go back and look at it any time you like in the future? Keep a memory box of first outfits, tiny socks, anything you brought home from the hospital, a list of who came to visit and when, a muslin square, a bottle of baby lotion to sniff, something you wore while you held him, anything at all that makes you think of your DS as a newborn. You won't forget but there's more than photographs to help you remember
And, if you can afford it, book a session with a photographer now, for as soon as possible, for some lovely shots of you and your DS while he is still tiny.