*hugs* I am so sorry for your losses. Nothing I can say will make it better, but I'll try. Know that what you are feeling is normal. It will take a while to feel any better emotionally. Know that's ok. It's normal, you are a grieving mother. Don't let anyone make you feel bad for it.
There is a set of tests that can be done to test for reasons. You can ask your doctor about them, but be aware many doctors won't do the tests until after three losses. (They can be rather expensive tests.)
Most of all, I'm glad you've found us, but sad you needed to.