Miscarriage with no bright red blood or clots?

So for about a month now I have been spotting Brown discharge. I got an ultrasound and they said the baby had no heart beat. I waited until Friday (which I was 12 weeks 2 days) and well the ultrasound tech said she “see no signs of pregnancy” including that she “does not see a sac.” How the hell is this possible? How is it that I miscarried without knowing it? No clots not bright red blood. Even the brown blood only amounted to a little bit (only there when I wiped.” Im so confused. I don’t understand. The ultrasound tech let me see the screen when she did the regular ultrasound (abdominal) but she didntlet me see the transvaginal screen. She also made me go out in the waiting room to see if the radiologist doctor that was present wanted me to do any more testing. I’m so confused. Like this would be my third miscarriage.