ultrasound question

Brittani • 29.. Married 2012.. Boy mama💙 and another 👶🏼 on the way!
I'm currently 27 weeks pregnant. My last ultrasound was at 20 weeks. I called my doctors office to see when my next ultrasound will be and they said that I don't need to schedule another one. Is it normal to not have one after the 20 week scan and not to have one in the third trimester? I have my regular appointments every two weeks starting next week.