Aww, Nic, its so difficult when you have a young baby.
Problem is, you are tired, and at only 4 months in, your hormones are still to pot, bf or not. He's also tired, and has had his life turned upside-down, and being a bloke isn't well equipped to deal with , 1 his feelings about A being in his life, both positive and negative, and 2 the fact that he's no longer your number one love (which lets face it, is true!). He does blatantly need to step-up, and man-up. He needs a good wake-up call, and i imagine that will come along at some point. Also, alot of men really struggle to find little babies that interesting, i know we all adore our little ones, and personally my heart just melts when F gives me that smile of her's, but essentially, they don't do much, and a good part of what they do do is kinda annoying (grizzling, waking up in the night, pooing on everything, vomming etc.). So you can see why, from a detached point of view, babies maybe aren't that great! Most blokes have totally fallen in love by the point that they come home from work and there is a little person pelting towards them screaming "DAAADDDYY" and tackle-hugging their legs, but that's over a year away still!
The other part of the problem with blokes is they never see the full story. They work hard all day, and it's tiring, and just because we are tired, that doesn't negate their tiredness, its not a competition. However, then they come home from work, and suddenly we are there, shoving a baby at them, saying "argh i need a break!" (ok, i'm exaggerating alot here, but there's truth in there!!) Then between the two of you, you bathe and feed the baby, cook dinner, try to get them to sleep, and get some quality time together/apart, etc. So, they only ever really see what its like to look after a baby when there is two people doing it!!
They have no idea what its like when you've spent 6 hours trying to have a pee and make yourself a cuppa, and failed on both counts because you are single-handedly trying to cope with a fractious baby, get the laundry on, prepare dinner and hopefully organise yourself out of the door to do a food shop, whilst trying to plan stimulating activities to enrich your baby's life experience, because that's what us super-mums are meant to be doing right? All of this on 4/5 hours of broken sleep! That underlined bit is really true, they just don't know that when they tell you you get breaks all through the day, they might as well slap you round the face! They say it, and then go and take a shower and sit down and plan a night at the pub with the lads and check their emails, whilst we stir the supper, with a baby on our hip, and wonder if we can get away with dry shampoo and "a bit of a wash" for the 3rd day in a row!!
Being a Mum is truly 24/7 365(6), and it never stops. Even when you go back to work, even when they are grown up, you will still constantly be a Mum. When you have a young baby who is totally dependent on you for everything, some days it can utterly drain you! Even if all you've done is fed, rocked and held a baby, it can still be mentally and emotionally draining, and the sleep deprivation (which is cumulative, and takes months to wear off once you get to sleep through the night) all add up to make it a bloody tough job!
Basically, Nic, in your case, yes, you do need to talk to him, because you need to find a way between you so that he doesn't feel put upon, but you feel supported. Try to work out what's the most important thing to you, and then find out what his priority is, and then accommodate each other. Also, i know i said he'll be struggling with the changes to his life, and maybe he doesn't appreciate that he does need to change his life, at least a little, to allow the 3 of you to operate as a family. That's where my OH definitely struggled. Also though, you need to have a soul search, and just check that you are also coming to terms with the changes in your life. I don't mean that to sound harsh, but from personal experience, its easy to overlook your own problem when someone else's is driving you up the wall all the time.
Making things work once there is 3 of you in a family, rather than 2 is about compromise. However much your OH is driving you mad and making you angry, the only way its going to get better is if you both work out what you want and need and then giving it to each other, or helping each other achieve it! Try to swallow your anger and talk calmly with him about how you can help each other.
Oh, and also accept that they pretty much never do things "right" when it comes to childcare. I find it best to set them a task and then DON'T WATCH OR CHECK on how or what they are doing!!! If you do, you'll only get frustrated with them, trust me! They do everything in the most difficult, crazy way possible! Somehow though, the babies manage to survive!
Anyway, i hope my replying rant isn't out of place, its just i've already been through it, and come out the other side (mostly, there are always relapses!!), so hopefully some of my rambling can help a bit!
It does really help to know that you also feel the same sometimes xx It may be the best thing that your OH gets to see how much work babies really are come Sept. I'm sure he'll pull through - A will show him the way!! 
)
Seriously justified rant. 
Also... my DH does that thing where he acts like I'm being over dramatic too! If I hint that he's not pulling his weight, he gets all snotty and sarcastic saying, "You act like you're doing it all, and I should be commending you for being super woman. But I assure you there are plenty of woman who have it a lot harder than you do." It makes my blood boil. I don't care if other women have it harder. That doesn't mean my efforts do not deserve acknowledgement or help. I work 40+ hours per week as the SOLE breadwinner for this family. I take care of making sure the bills are paid and household necessities are in order. Apparently I am the only person in the house that knows where anything is since he cannot manage to do anything without having me tell him where things are. (P.S. The babies clothes are in their dresser just like yesterday and the day before and the day before!!) I am also the SOLE nighttime care giver for my babies. So, yes, damnit! I DO think I'm superwoman! 
And this is why I love this group of mamas.
