This is incredibly common.. It may take some work to get past it however.

Men Tend to think in two ways -
1 - as you said, he did see something graphic, and what looked like probably hurt you quite a bit.. and following that..
2- He may be afraid of hurting you after seeing that, because men tend to be very protective.

Best thing you can do is sit down and talk it out. You may even want to go so far as doing some exposure therapy If you are the adventurous type.. You dont have to have sex, or even really fool around, but perhaps if he is able to see it doesnt look like that now nor are you hurt down there now, it will help to ease his mind.

I would confront him on his making excuses though. I wouldnt be mean about it or anything just say "it feels like you have alot of reasons to not have sex right now. I think we should talk through that"

Also try googling "husband doesnt want sex after baby/birth/childbirth....

Its extremely common!