This won't be a popular opinion, but my advice would be to stop breastfeeding. I had really bad PND and was struggling with everything, especially breastfeeding. I was exhausted and DD had problems latching, my boobs were always hurting and I was not coping well, so after one month I switched to formula. She slept for longer and
I wasn't up all night breastfeeding. I was still struggling, but it was one thing that helped a bit.
I went and got some counselling sessions for my PND, tried to get some sort of routine where I was getting out of the house enough, napped when DD did and just did the bare minimum of housework.
It will pass OP, you feel desperate and exhausted, but time goes on and things change. I remember I used to dread going to bed because I was aware of the sleepless night and night feedings ahead and dread getting up, because DD was colicky and cried most of the time she was awake. Now she is nearly 9 years old and those times are just distant memories. You will get through it OP. I found the baby stage very hard and decided not to have more kids because I couldn't go through that again. I really feel for you how tough and isolating it is. It gets so much better, honestly.
Re the nappies, I would go up a size, they generally leak because they are on the small side.
Look after yourself and try to have some you time when your DH is home to help. Watch a
bit of a series, read a book, have a bath, have a nap, do a face mask, whatever you like, and leave him with the baby for an hour or two.