4 miscarriages and all tests inconclusive

[Luvbug4]

I have had 3 missed miscarriages (body thinks it's pregnant for 8 to 10 weeks but baby doesn't develop past 6 1/2 weeks -never a heartbeat) and 1 chemical pregnancy.  I have had 3 D&C's and miscarried the other on my own.  I have no problem getting pregnant or sustaining a pregnancy it's just that my baby has a problem developing.  All of my levels are said to be normal and just to be on the safe side they gave me progesterone to further support my early pregnancy.  My HCG levels rise as they are supposed to.  No Genetic defects so far?!?!?!  I can't afford IVF right now but that isn't even a gurantee.  
Are there any suggestions as to any other tests they could have missed or I should have done?  It is NOT an abnormal uterus, don't get blood clots, my body doesn't attack the baby, and my levels and the chromosome tests are all normal.  I am getting frustrated because this is taking a big toll on my body and emotions.  Any doctor out there that wants to take a guess at things let me know.
Thank you for your time and may 2009 bring many blessings. :)