Can I ask for an ultrasound?

Abigail • Pregnant with #2 & twins this time!
I'm worried because I felt my movement in my tummy a few weeks ago and now nothing. Also, at my last check up, my doctor only heard one heartbeat but said it's normal because they could either be extremely close together or one could be hiding in the back. I've been so worried ever since though. Can I ask for a sonogram and they have to/should give it to me?