2nd miscarriage...WHY?!? what's wrong w/me?!?

I'm 18 years old--in the prime of my life! I'm incredibly healthy. In my "healthy" weight range. Eat well, sleep well, exercise well. ect. ect. In December (09) my husband and I lost our 1st baby at 11weeks pregnant. We got pregnant again a few months later and I just found out yesterday (15 weeks) via sonogram...that there's no baby in my womb. I think it died at 10 weeks and reabsorbed into my body. (I had a lot of bleeding at 10 weeks...) Obviously we are able to concieve--that isn't our problem. But does anyone have any ideas why I am losing them? The drs won't start to run tests and see whats going on until 3rd miscarriage...so please don't say "go to a doctor." I guess i'm looking for some encouraging stories or advice. I'm frusterated and heartbroken. All I want is a baby.