gestational sac cannot be seen

I took my first round of clomid on cycle day 2 to 6 n got a very very faint positive on the 24th of Dec ,AF was due on 25th of Dec but it never showed up. I took a test again on the 26th of Dec n got a BFP. I went to the hospital on the 28th for my first scan n was told the gestational sac cannot be seen. my doc has rescheduled my next scan in two weeks. do u ladies think I went to the hospital tooo early or there is sometin wrong?? pls I need answers cos am getting worried