"Part of me thinks I'm just hoping it's PND so I have an excuse for being so crap, then another part of me wonders if that's PND talking
"
I so know what you mean! But, at the same time, it's OK to be crap sometimes. You're doing a difficult job that makes huge demands of you.
I've just been skimming through a marvellously misogynistic medieval book and came across a section on the supreme importance of sanctifying the Sabbath with resting. It states categorically that a woman from the moment she goes into labour until 7 days after giving birth should be given whatever she wants, even if this means breaking the Sabbath rules. And this pampering continues for another month.
I am glad we live in our enlightened modern times, but I think we've gone wrong with our post-natal expectations.