Oh Jus you poor thing I know how hard it's been for you and you have all my sympathy and support. Just for the record- and i like to think that having seen you in person and having a social work degree I'm a reasonably good judge of this- I really don't think you have PND and you are, as you said, just sleep deprived, stressed and exhausted.
I know what you mean about people saying 'oh she's such a good baby' and feeling bad because you are not feeling like you're coping- I get the same thing with Ty and I think to myself 'lots of people have it worse than me- am I just feeling sorry for myself?' and as I've said to you, it's all relative- Ella was an exceptionally easy baby for weeks there and now you are going through this it's so hard because it's new- if it had been like this the whole time you'd either be in an asylum or really blas'e about it by now ykwim? You are doing a fantastic job and doing what you can and being an amazing, selfless, kind, caring and compassionate mum- better than to be expected at the moment!!
Trust your gut instinct with Ella's health. It might be one of those things that resolves itself before you even find out what it is but give yourself a pat on the back for having the instinct and trying to find out what it is.
Going for a walk's a really good idea- always cheers me up. Speaking of, if you want some walking company come knock on my door- I'm always up for it and I might even get a sleep out of Ty!!
Also, if you ever need some help or just someone to have a coffee (or some kind of dairy and caffeine free beverage and a chat and a cry with, I'm here for that too. Tony can take Ty in the arvos, he's home early, and I'd be more than happy to sit with Ella for a while while you get stuff done or do it for you- I'm a suprisingly good and quick house keeper
I'm here if you need me. I know you've got heaps of support but I'm just throwing my hat in the ring too- too much support is not a bad thing.
In the meantime, huge hugs for you. Please know that you are a fantastic mum, Ella is a beautiful bubs with her own distinct personality and you are doing the very best job you can.