Shocking News!

I and my hubby were shocked by the news when I did the ultrasound and the amnio test on March 24 in the hospital==> I am having twins!There is no family history having twins in either of our families.The first ultrasould was done when I was in 12 weeks in the hospital referred by my previous OB doctor, they told me my baby looks good and that was in 12 weeks back then. Is there anyone knowing about twins, I am really curious if my babies are identical or not. The doctor told me there is only one sec for my twins which means the twins are from one egg.