Your reactions MAY be totally normal healthy reactions to losing a life you enjoyed and having this huge burden placed on you. On the flip side, maybe you are reacting in a somewhat abnormal way to the changes in your life.
I agree with this. There are lots of respects in which our culture's way of 'doing' childbirth and parenthood fails to support new parents, especially mothers, very badly. You spend 9 months going through what is for many a complete physical ordeal, and - the first time, at least - you talk glibly about 'getting your old body back', and others, who often should know better, talk in terms of 'getting back to normal'. And the whole time, you're being checked out regularly by a midwife, plus/minus other HCPs, who make you feel special and cared for, and people are congratulating you and offering you their seat on the bus, etc etc. And then, finally, this baby is born, and following a brief period of home visits, the door closes on the midwife and the health visitor, your DH goes back to work after a few days off to help, and you're left with a baby you may or may not have got to grips with caring for and a body that will never be the same again. In lots of respects, I think PND is a completely sane response to an utterly mad way of inducting new mums into parenthood. Other cultures do much better.
I remember this happening to me so well. After DS1 was born, I remember sitting in the bath one Saturday afternoon, and suddenly realising my old body, the one I had so been looking forward to getting back, was gone for good. What was also gone for good was the baby I had imagined I was carrying. That 'dream' baby I had spent 9 months imagining and looking forward to meeting was gone for good, and what had replaced him was a real-life version that was a hell of a lot noisier, less inclined to sleep and putting me through hell in my determination to breastfeed. He looked wrong, felt wrong in my arms, and also had apparently brought my life as I knew or imagined it to a screeching halt. I can look back now and tell you that that is what I sat in the bath and cried about, but at the time all I could think of was running away. When DP asked me to explain, I begged him to consider putting the baby up for adoption, so we could 'get back to normal' (as if we ever would have). Normal, in my mind, manifested as being able to drink coffee in an unhurried way in a European city (!?). All of this is not such abnormal 'help, I've had a baby' stuff, but actually was not entirely normal either, and thanks to the lack of help I received, culminated nearly a year later in DP having to stop me from walking out into traffic 'because everybody would be better off without me'.
So please, OP, get some help. What you are feeling is partly valid feelings of unhappiness that need working through, but almost certainly partly illness too. Please don't let things get to the stage where your DH and DS are having to cope without you.