Hi Jennifer,
I'm so sorry for your loss. I felt the way you do now. I was on top of the world, then I started bleeding. I had an ultrasound which was devistating. They really need to give those techs some sensitivity training. Then I had surgury where my left tube was removed. In the aftermath, I just felt so robbed and so empty.
I did have an HSG. I just felt like I needed to know that my other tube was clear. I had not had any children at that point, and didn't want to waste 6 months TTC if my other tube was blocked. I was able to conceive my DD right away after taking 3 months off. It doesn't happen so easily for everyone, but there have been quite a few sucess stories around here.
Backing up to your first question about follow up HCG. It's probably best to discuss it with your doctor. I believe that my doctor considers anything over 5 to be PG. Under 5 is not, but I would talk with your doctor about it.
Chances are, there is nothing that you did to cause your EP. I went through the same thing. Did I work too hard in the garden? Should I have quit Yoga? I don't think we can do anything to cause it. It is a fluke for most women, and chances are it won't happen again. Since you already have a DS, you don't likely have a tubal defect.
I'm sorry your DH doesn't understand.

He needs to know that your baby was real and you could have died. That is very traumatic. He may just be in denial. But for your sake, he needs to be there for you. We're here for you as much as you need us. Please feel free to post as much as you need to.