Hi OP, just bumping for you.
I'm pretty sure I had PND but never sought help for it - something I regret now as I often wonder whether the early months could have been different. So I think being open and getting a diagnosis is a great first step.
If you feel up to getting out of the house, then definitely do that as there are all manner of studies on the positive effects of fresh air, sunlight (well...
), exercise etc. At the same time, I do recognise that it can be hard and it's by no means a magic bullet.
Ultimately, it's about surviving as best you can and going easy on yourself. So first of all, ditch all the little pre-baby things you think you can do without. For me, that was mostly housework and plucking eyebrows etc.
Try not to give in to feelings of guilt - almost all mums feel it and it doesn't mean you're failing (if anything, the opposite).
Don't be afraid to ask for help whenever you think you need it - don't just struggle on because 'I used to be able to do this' or 'X can do all this and more.'
Remember that, sometimes, you have to look after yourself first in order to be a good mum to your baby.
Don't know if any of that is helpful...