I’m confused

Hey guys I was wondering if I can get any help from you guys. So I had my first ultrasound when I was 7 weeks and now I’m about to be 12 weeks and the doctor was supposed to call me to reschedule and never did. I have called them every single day for the past week to see when I can get seen and they still haven’t given me an appointment also they said that for my next visit it’s not going to be an ultrasound. So my questions is how often do I need an ultrasound? Shouldn’t be once a month or am I wrong.