I think a lot of us have these same fears, and it sucks. I have come to the conclusion that the only rational and sane thing to do is to take it one small step at a time, without thinking too far ahead about "what ifs". I know that is hard to do, especially with your loss, and being in the tww is emotional. But I have decided that if I didn't stop doing the "what if" game, I was going to go crazy and stress out to the point that it may hinder pregnancy even more. So just focus on the tests and be positive that any results will get you one step closer to conceiving again. Only after that point should you worry about what the dx is and what drugs you will need to take. And then the worries about what to do if the drugs/procedures don't work come after that, but they are at least 2 or 3 months away from now, so don't stress about it now when all it does is hurt you.
That is my voice of reason, but I do completely relate to how you feel. It is hard, and your feelings are so normal. Even knowing I shouldn't get too worked up about things that aren't on my plate right now, I do sometimes. We all do. But we are here for you, and I firmly believe you will get pregnant again, carry to term, and be the BEST mom to your child!