Sorry you’re feeling like this.
I hope this doesn’t come across as patronising, but it seems you know what you need. That’s the bonus of having been through this before….
To leave the house daily.
To cook and eat at least one meal a day that’s quick and healthy.
Sleep.
To feel like you’re good enough.
To address stuff that needs doing (putting off phone calls lets “little” things- that don’t feel little at all- build into massive things and adds to the stress and feeling of worthlessness)
The next step is finding “easy” ways to do those things, and the step after is pushing yourself to do them when you don’t feel strong enough.
My suggestions-
Meals: pick things that you can prep at nap time, or leave to cook. Filled pasta/ sauce/ salad. Sausage, pre-made mash, veg. Bag of casserole mix veg and chicken. Slow cooker chilli (with micro rice one day, nachos or jacket potato the next) Do a week plan and make shopping lists so you only have to think about it once.
Go out: walk to buy nappies/ milk - start small. Walk to the library to pick a book. Playgroup when you feel braver only. Go out for dinner ingredients. Feed ducks.
Feel like you’re good enough: read the comments here. Notice how well your dc is doing- that’s all you! Treat yourself daily- bubble bath, bed with a book, a little chocolate, paint your nails, light a candle, put clean bedding on, whatever - this is very important and should be prioritised over hoovering/ cleaning again/ mumsnet at nap time or after dc is in bed. Smile at people in the street/ in shops or call a friend- connection helps
Make a to do list (this is scary) and do one task each day, then reward yourself. On bad days, pick easy ones!
Do a tick list on your phone each day: leave house, decide dinner, make dinner, treat self, tick off a task. Feel proud of yourself with each daily achievement.
Sleep. This comes when the rest falls into place, but meanwhile somethings help…. Fresh air daily (see above. Or coffee in the garden under blanket!). Exercise- walking is enough, even just 5 minutes for now. This works sleep spray- I swear by it. Put the bedroom window on vent. Get a weighted blanket (not if you bedshare). Keep a pad of paper by the bed if you find your mind going into overdrive and put your thoughts on paper to save for later. Accept that sleep is still sleep, even if broken by your baby waking, and that this won’t last.
You can do this.