The fourth trimester is hard, and only made harder by having excessive expectations about what can be done. Your own expectations, your partner's, a combination of both.
I have 3 DC and still regret not "getting it" with my first and not just accepting what the 4th trimester is about.
Basically you have a baby that had to be born. Human brains have become so big the baby has to be born at around 9 months or it wouldn't get out. But other than that nothing has changed! You have a very dependent infant. For the next 3 months it's as though you are still pregnant but you don't have your hands free anymore. Baby wants to be with you, be held by you, and if you are breast feeding, wants to feed on demand like it still has the cord attached -small feeds, big feeds, comfort feeds, feeds to fall asleep to....
And that's it really, 3 months of sitting, cuddling, comforting, feeding, sleeping next to your baby. What you need most is to accept this, enjoy it for what it is -it's not a long time in the scheme of things. One day you will miss it, hugely! And you need a partner who accepts this too and isn't thinking "oh wow, paternity leave, I can get all those DIY jobs done, and when I go back to work my wife is at home making me packed lunches and dinner every day!". He needs to know he's going to be stepping it up too -getting laundry on before work, bringing food home at the end of the day etc.
First time round it's a bit mindblowing, even overwhelming, OMG is this forever etc....with subsequent children you'll be watching the weeks tick by knowing all those quiet snuggly days are going to come to an end all too soon.