Oh Jus, you poor love. What you typed at 4 something this morning could have come from me at that stage.
I did the same as you though. Made it a priority every day to go for a walk. Improved my general mood no end.

Lana also gives fantastic advice and in hindsight is what happend to us, we just didn't see it.
I had an epiphany at around 7 months. My world was caving in just because of basic sleep deprivation. When I decided to step back and do what Darcy needed, not what everybody said she needed - it got easier. I laid with her, I co-slept, i wore her in a sling. I have spent many hours holding a hand next to a cot. At first it was a pain, but then I started to think about that time differently. Now I meditate or read if I'm stuck next to her bed. Like animals they take their emotional reading off you and if you're stressed - they're stressed. Finding my zen helped my bubba find hers.
Unfortunately my PND and OCD got worse, but at least I was getting some sleep.
I didn't want to take drugs either (different reasons to you though - i'm a cop and they would have taken my gun away - preserving my work persona was my last peice of normality in my world at that stage). I worked really hard with a community health counsellor and with the walking was able to get my life back under control.

I believe you can do it too. Ask to speak with a counsellor if you feel you need to - even if it's to verify that you don't have PND.
Belive in you. You are a great mum doing all the right things.