Ok - so the doctor's office called with a result. I don't know if this is the only result (if all the tests are in yet), and we're still planning on checking my tubes next week, but this is the one the doctor suspected. This is the one she said was probably clotting in the placenta and cutting it off from the growing embryo, thus killing it.
Apparently, this is a clotting disorder with all kinds of issues. It doesn't allow the body to process folic acid properly (so even though I was on a double dose for years, it did no good), and often results in preeclampsia, placenta abrupta, recurrent miscarriages, and low birthweight and early babies (hey, that sounds familiar). In some of my research, this seems to indicate that there's a higher possibility for having a baby with spina bifida, but this is very scientific and out of my league, so I'm not entirely sure. Perhaps that is why there would be so many sonograms?
In any case, the second I get my next positive pregnancy test, we hit the road running. Apparently this involves a daily injection of blood thinners and some other precautionary things like frequent sonograms and check-ups. I'll also have to be very careful with my movement/exercise/etc during pregnancy since it is so likely to cause the placenta to tear.
We'll hope this is it. I mean, we now have some serious thinking to do about whether or not this is something we should proceed with, but the doctor says she has three women on this regimen right now who are doing well. We would have to really watch strenuous movement, sudden movement, any bleeding - since I'd be on blood thinners, and the delivery has to be carefully planned due to the blood thinners.
It's a lot to think about, but it's a start. Thanks for all the good thoughts and prayers.