I totally agree with everything adgal has said, if indeed you have miscarried again, its time to have some tests done, they will probably start off with routine blood tests first, you could simply be low in vit B6 or vit D, that can cause miscarriage, also have a pap done as there is a bacteria that can be in your vagina that can also cause reocurrent miscarriage, it can be a very emotional time, but now is not the time to give up, take the bull by the horns and fight for the baby you deserve :) good luck
I am so very sorry...you are in that horrible wait and see time. Yes, sometimes losing symptoms overnight can be a sign of loss, but not necessarily. Even the bleeding doesn't really mean a loss..lot's of women have first trimester bleeding and all is fine.
As for what could be causing this. If this is indeed a loss, that makes 3 in a row. Most Dr.'s will agree to further testing at that point. Sometimes it can be just plain old bad luck. Other times there can be an underlying issue such as a blood clotting disorder (just to name one possibility). Fortunately, in most cases, the medical issues causing a loss can be dealt with. I'm like you. I conceive very easily, and just suffered my 8th miscarriage. I had 5 in a row, then a healthy little boy, followed by 3 more. In my case we are fairly confident it is age related. (I am 42, and was 38 the first time I conceived). It can feel like a cruel joke. Being young and healthy helps. Ask for testing and rest assured that it is very likely you will indeed become a mom.