Ultrasound problems

My doc pissed me off... I had one ultrasound at 7 weeks and 4 days then she says I won't get another one until 18- 20 weeks for anatomy scan..i had 2 miscarriages last year and she doesn't think I'm medically indicated for another until then. I'm confused and frustrated..i shouldn't have to pay out of pocket for it. I have Medicaid.