I had one shortly after I found out I was pregnant which is where they determined me 7 weeks 3 days and then I had one at 12 weeks 3 days for the genetics screening and I have one scheduled for the 19th of this month when I will be 18 weeks 4 days to find out the sex of the baby.
My large doctor's practice with 7 busy doctors gives one ultrasound as protocol. While it is fun to see the baby, it's unnecessary and drives health care costs up. I did have a second ultrasound with my second child as I began bleeding with clots. I'd was diagnosed as lots of ladies are at my first ultrasound that I had placenta previa (which for the vast majority of women lifts as your pregnancy goes on)-- so they wanted to check since I had started bleeding. Everything was all good and it was a fluke bleed. Anyway, unless there is a reason, many medical practices responsibly do not give multiple ultrasounds. I try to look at it that way rather than being disappointed that you don't get to view baby more often. :>)