Well the reality of your situation is that DH doesn't want a third child, and he has every right not to want one, just as you do to have one.
And you can't make him want another one if he doesn't want one.
I understand it must be hard for you if you feel you really want another though so I do feel for you.
But your choices are, find a way to deal with being happy with the little family you already have, and stop daydreaming about having another, or you leave your DH, split your family up and try and find someone else to have a 3rd with. Which I am going to assume is that last thing you want to do, and not really an option that you want to take.
You need to find a way to reframe your thinking. Think of all the lovely things that your little family now gets to do, and the freedom this will give you in a few years to have a little more time together as a couple and the lovely family times you have ahead of you. Plan nice things, days out, Birthdays, Christmas, family times at home, things you do together to make memories together with the kids that you will still all talk about when they become adults.
The newborn stage is nice, granted, but the best, IMO, is yet to come.
Stop picturing the bassinet and start picturing other lovely scenarios with your DH and the DC that you already have.
And the newborn bubble is a myth and I don't know anyone who experienced this, so I think you need to give yourself a reality check there, and if this is really making you depressed then I think you need to get some kind of counselling to help you come to terms with the sadness and loss that you feel, and enable you to look to the future without another baby in it.