Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice.
can happen due to many causes.
According to your description, you ruled out progesterone deficiency
as your doctor supplemented and also uterine anomalies.
Now the possible causes are genetic abnormalities, more in consanguineous marriage.
If you have done DNA testing of dead baby, that can give some information.
Then you have to rule out infections, TORCH panel testing is advised.
Also better to test for antiphospolipid antibodies
Sometimes cervical incompetence
can also lead to miscarriage, especially in second trimester.
So, better to test for all these things with your doctor's help before planning next pregnancy
Hope I have answered your query. Let me know if I can assist you further.