No ultrasound until week 18?

I'm currently 9 weeks pregnant and just had my first doctors appointment the other day. she said everything looks good and healthy. Im just confused because she said I'm not going to have my first ultrasound until 18-20 weeks. Is this normal? Isn't that pretty late for the first ultrasound considering thats the time frame you find out the gender? My doctor said it was because I knew the exact date of my last menstrual period so there's no need for one sooner. I see everyone getting ultrasounds at 8,9 & 10 weeks so I'm pretty bummed. Should I ask my doctor if I can get one done sooner?