Maybe twins?

Just had my first prenatal appt today at 13wks.  No ultrasound was done (it's scheduled for June 9th) & the doctor found the heartbeat immediately so he didn't go searching for another one.  But when he was giving me my exam he said my uterus felt larger than it was suppose to for 13wks, that I felt like I was 15-16wks.  I'm positive of when my last period was because it came on the day after something important happened to me.  Hoping these next two weeks fly by so I can see my baby (or babies).  Has anyone else been told their uterus felt higher for their gestionation week & ended up having twins???