Kristi,
First, I am so sorry about your loss. I am also sorry that it seems like your DH isn't being very supportive of you during this difficult time. I think I left you a message on the First Tri boards. I still really think this sounds like an ectopic, but being that I'm not a doctor, I can't say.
I would strongly encourage you to tell your husband how you really feel, and also be up front with him about what you need in terms of support. A lot of men don't get subtle hints, and this is a time when he needs to be there for you. When I had my ruptured ectopic, and was told I may never be able to have more children, I was really devastated, and was a total wreck. If I had told my DH I need support, he wouldn't have the slightest idea what I needed or wanted him to do. But if I told him I really need a hug, back rub, help washing my hair, etc, he was very happy to help me in any way he could. But, I had to explicitly communicate my needs to him. By allowing him to be there for me, and help me, he didn't feel so helpless, and I think it helped us to feel more like a single unit that came out stronger on the other side because we made it through together.
I think you should also discuss how much it would mean to you to have a second child once you have given yourself the necessary time to grieve and heal. If you try and talk too soon, your grief and intense emotions right now might get in the way of trying to see your DH's point of view. I don't agree with him necessarily, but I do always think that you should try to understand your spouse's perspective in a disagreement about something this big, just as he should try to understand yours. If you can't come to an agreement, then you need to consider whether you would be happier moving on and trying to have another baby with someone else, or staying and being content with your DD and step daughters.
I have had 3 losses myself, and I do understand your emotions right now completely. Personally, I felt that giving up trying for another baby made the ones I lost be lost in vain. i wasn't willing to quit trying until I hit menopause if that is what it took. The journey to becoming a parent isn't always easy for everyone. My DH and I had to sit down and have really hard discussions about our family plan after the losses. It really took a lot of open and honest talking for us to figure out how far we were willing to go to keep trying, and what would happen if we weren't blessed with a second child. I really hope that you and your DH can come to an agreement that you both can live with and without regrets. Good luck to you, and please keep us posted!