Am I having twins?

I am 6 weeks and recently had a transl ultrasound done. It showed the baby and I heard the heart beat. But when the doc moved the probe to the left, the sac turned into what looked like 2 separate sacs! I asked if I was having twins and she said it looks like it. She tried to get a better image on it but couldn't. We didn't see a baby in this second sac, that is if it is a second sac. Whenever she moved the probe back to the right, the second sac merged back into the one sac with the baby, and she's move it again, and again it looked as if it separated into two sacs! What do you think?