I had 5 miscarriages before carrying my two kiddos. I has a regular OB who wasn't concerned I had 3 miscarriages and wasn't going to do any testing until I had 5 or 6 miscarriages. I then went to an OB who specialized in high risk pregnancies. He did a bunch of testing and made me feel like I wasn't crazy in questioning why I kept losing my babies.
Please consider changing docs. You're completely normal to be somewhat anxious. You should not be brushed off. I would call them and tell them you want the u/s early. If they give you grief, ask to speak to a nurse and don't back down. It's your body, your pregnancy, and your peace of mind. They don't get to call all the shots. If they get mad- too bad. You're not there to be their friend. But I urge you to consider using a high risk specialist.
When I thought I was pregnant with my son, I went to the maternity ward at the hospital (we had just moved to a new city and didn't know anyone to ask) and spoke to delivery nurses and asked them to recommend a doc. When I called the office, I was told it would be at least 6-8 weeks before I could get in. I called my specialist in Dallas (who successfully delivered my daughter) and he called her directly. I had an appointment the next day.
Hang in there. Please let us know how you're doing.