Ok - if you want this thread to be about you then you need to find a way to let go of the resentment you feel about how he treated you in the past.
Someone suggested you have a once and for all vent about how unsupported you felt to a trusted friend.
I personally would prefer that vent to be towards the unsupportive DH directly.
When DC are occupied I’d literally sit him down and spell out how you feel:
behaviour after childbirth, feeling unsupported, behaviour when you were ill
But it’s a ONE time thing ie you need to be prepared to let it go once you have expressed it and then put it behind you.
Then you need to talk openly about your current set up. Acknowledge that he is in pain and you are sorry there is not an immediately obvious solution.
However, his issues do affect you and you find it hard too and it’s affecting you. Explain how it does impact family life and while you understand he can’t help it and didn't choose it, he needs to be a bit more mindful that it’s hard for you all the time with worrying about him and having to manage DC and household stuff. Tell him the constant discussion about his pain is hard to hear all the time and takes a lot of your headspace, something you don’t have a lot of.
It might be performative moaning but it might be a case of a complete lack of self awareness. Sometimes people just need to be told/prompted to have a think about how they come across. In the framework of a marriage, these conversations should be ok to have and they can be firm and factual, while delivered with kindness.
Otherwise I fear the resentment will eat you up.
After that, the next goal I’d suggest is him learning how to be able to look after both kids on his own. In whatever form that takes; in accordance with his health limitations. The current set up is totally unfair on you.
Once that is sorted - you really should treat yourself in some way - perhaps a short break away from both DH and DC so you can centre yourself a bit.