NO YOLK SAC & FETAL POLE

Hi
My L.M.P is 21st Dec'09
i confirmed my pregnancy on 1st Feb 2010
I took U/S scan on 4th feb 2010 it showed nothing in the scan but HCG level in blood test was 1000
Another round of U/S which has higher resolution scan taken on 6th Feb,it showed traces of yolk sac but doctor was not 100% sure.
Doctor asked me to come after 2 weeks,so took on 20th Feb 2010(7 week 2 days as per scan results) it showed just gestational sac but yolk sac & fetal pole was not seen.So doctor asked me to wait for another 2 weeks for some good results to be shown if not seen doctor asked me to do D&C.
So i am worried so much, i don't have any bleeding but still why this problem persists?
I would like to know the reason as why yolk sac & fetal pole not seen for 7weeks 2days,is it too early to detect?
please help me out