A little confused...

Ok so when I was pregnant with DS I had an ultrasound at 10 weeks to confirm and then an ultrasound every 4 weeks until he was born. Now almost 16 weeks and I had my first ultrasound at 10 weeks and my Dr office says I won't get one again, I'm just a little confused as to if this is normal because I thought they were supposed to be measuring baby as it grows to make sure it's growing properly. Any thoughts? I'm thinking about changing Dr's because this isn't normal to me