Ultrasounds

Hi! How many ultrasounds are you supposed to get throughout your pregnancy? I got my first at 8 weeks, but didn't get one at my 13 week appointment. I was sooo disappointed. The doc used the Doppler to hear the heartbeat, and I told her I couldn't hear it. She was like, "oh well I did and the baby is healthy"... Didn't get the HR or anything either. She didn't even take note of it. Blah, I'm just really annoyed.