Asked for a post-mortem examination?

I didn’t know about this examination :( Also I don’t know if a 14 weeks old foetus can still be examined? The doctor isn’t sure about the cause either and despise my researches. I suspected it was caused by infection in my body after I got diarrhoea. Because I kept getting chills during my pregnancy. I severely shivers everyday since the second month :( Doctor kept saying that the shivers was caused by hormonal changes. But I knew it wasn’t normal. Because during the first month, I always feel hot. After I gotten a diarrhoea, my body started to shivers terribly. I really wished to meet a doctor that can communicate well, at least recommend blood or fecal lab test. Now it’s too late already. The baby has died