Bad ultrasound - need advice - sorry long

According to my last period on dec 21st, I am 8 weeks 4 days pregnant. Using an ovulation test kit, my ovulation started 1 week after period on dec 29th - which is a day we also had sex on. I had an ultrasound today - first abdominal but didn't see much so did a vaginal. The tech said I had a tilted back uterus. Then didn't say anything, after we were done she left the room for what seemed like forever, came back and asked me to go to the OB department. The doctor i saw (not my OB Doctor) said I had a miscarriage. He said he baby measured 7 weeks 4 days -- meaning I concieved on dec 29th right? He didn't say anything else as to why he said miscarriage, I'm assuming the tech didn't hear a heartbeat because we didn't hear one at the appointment. I was in too much shock to ask the doctor any questions. Doesn't a tilted back uterus make a heartbeat harder to hear? Should I have a second opinion? My OB was already out of the office so I assume I won't hear from her until Monday. I am just so confused because to me the baby is measuring right on schedule but there is the question of why no heartbeat. I have had zero spotting, very mild cramps but only a few times, and had normal for me symptoms. I am a first time mom and just so unsure what to do here. Thanks for any help or advice.