Is Transvaginal Ultrasound Advisable During Early Pregnancy?

Hi, doctor i Wil appreciate ur kind advise.. Thanx. I missed my periods this month feb 2015 and date of period was 3feb. I did home pregnancy test it was positive. I saw my gyno at 9th feb and she did ultrasound but nothing was visible. She called after 1 week at 14 feb and that day she saw only sac. She gave me duphaston 10mg 2 daily and she call me on 21 feb for transviginal. I m so confused isnt that so early for transviginal ??? I want to tel u that I never had miscarriage before?? I m thinking to see doctor after 2 weeks may be at that time everything will be visible at normal ultrasound... Plz advice what i should do?