First ultrasound not till 17/18 weeks

I had my first doctor visit the other day right when I hit 12 weeks, I got to hear the heartbeat which was amazing, but the doctor said i won't schedule my first ultrasound until my next visit, which I will be 15 weeks then, then after i schedule it it will be another 2 or 3 weeks. And i see women on here having ultrasounds at like 8 or 9 weeks and it confuses me because this is my first pregnancy so I'm not sure what's normal or not.