Reaching out for help is a sign of strength and not something a 'loser' does
- that alone shows that your are a good mother to your children.
Stop beating yourself up - you are struggling in a very difficult situation, you don't sound v supported by your DH or HCP, so stop being hard on yourself.
Parenting 'normal' children is the hardest thing anybody will ever do IMO and IME - you have 2 close together, another one on the way: you need help NOW, before the new baby arrives.
Yy to deliberately seeking time with your DD: hold her, cuddle her, sing to her, look at picture books with her, even watch some CBeebies with her on your lap etc etc.
You sound so sad and defensive, rather than proud of your achievement of having got through a really tough time - that took strength. I've been there with term DS1 followed by preemie DS2 12 months later - he is now 10 and I still shudder at the memories.
See your GP, speak to your HV, attend a SureStart Centre, could you consider a Mother's Help for a few hours a week? The help you need is out there, but you do need to make the first step and reach out for it.
Would it help if you showed your DH this thread?
Be very kind to yourself.