Chesapeake - Any number of problematic things can happen in early pregnancy, causing the body to naturally abort the baby, as your body knows something is not right. And just because you have a healthy child doesn't mean something just didn't work right this one time when conception took place.. if you really research (don't, not at this time anyway), it's amazing anyone can procreate with all of the things that can and do happen in early pregnancy for so many women. This is why it's stated that many women get pregnant much more often than they realize, only to lose the pregnancy before their AF's are even due (chemical pregnancies). I know that didn't happen to you though.
I am so sorry for your loss. I've had four. It's not easy, I know. I think it's fairly normal (as sick as it is) that many women have at least one m/c in their lifetimes.
And usually until it's 2-3 m/c's or more, dr's won't do any testing. But if yours will and it will help, then definitely do it.