What Causes Nausea After Miscarriage?

I recently found out I was pregnant after having a miscarriage (d&c) on August 6th - with no last period to go off of and no clue on date of conception I had no clue how far along I was, so they did a blood test Friday my hcg measured 12,000 so they scheduled me for an ultrasound today, based on her measurements the US tech said it looked like 6 weeks but there was no heartbeat and there was an enlarged yolk sac. She immediately brought in a nurse who apologized to me and called it a nonviable embryo and asked if I wanted medication or another d&c. I was in shock, didn't even talk to the doctor. That's it? Just like that it's over? I've done a lot of research and a heartbeat is NOT always seen at 6 weeks and an enlarged yolk sac does often lead to miscarriage but there ARE cases of women who go on to have normal pregnancies. I understand the odds are stacked against me and yes this could end up being a miscarriage but I do NOT believe in terminating the pregnancy until we are 100% sure which at this point I don't not believe is the case. I am demanding to speak with a doctor and have a follow-up ultrasound in a week. They are acting like I'm being silly and filling myself with false hope BUT I have heard of too many cases of misdiagnosed miscarriages to just end my pregnancy immediately without a follow-up to be absolutely 110% sure it's nonviable. I'm having no cramping and no bleeding and I'm incredibly nauseous and have been for a week and a half now.