Wow, you've been through so much. I'm not at all surprised you're affected by what's happened to you.
Again, I don't know if it's PND or not, but whatever it is I really think it would help you to talk to your GP or HV. They will know.
Have you told your OH about how you feel that he's out so often? That would really upset me too, I think it's pretty unreasonable of him to think it's ok to be out all the time, especially if you are struggling for money. Be careful how you word it though if you've been arguing a lot lately.
I don't think your feelings are as hard to understand a you might think. I remember when Frankie was a few months old, I sometimes used to feel sort of empty. Not desperately unhappy or anything but I was very worried about why I want ecstatic as being a wife and mother was literally all I had ever wanted but I sometimes felt a little unfulfilled. I hated feeling that way but it turned out to be just a phase, it only lasted a couple of weeks. Hopefully it will be the same for you xx
PS I think all mothers worry that they are not good enough. And EVERYBODY worries about leaving their baby xx