In our office (In NY), we do one ultrasound to confirm pregnancy if the mother wants it and that is usually done around 6-12 weeks gestation, and another around 18-20 weeks. Then, one toward the end to confirm position, fluid, weight, and things like that.
It's not abnormal to only have 1 U/S. I'm sure if you truly wanted one, you can complain about pains, or something and they may do one! LOL!