should I be worried?

I am 8 weeks pregnant with my first child. I had a vaginal utrasound at 6 weeks to see how far along I was and everything looked great.  Last weekend, I had some spotting (no cramps) so my MD did another US.  This time, the heart beat was detected, but the gestational sac had not grown. The baby is at 8 weeks, the sac at 5.  I do not have any symptoms at this point other than being a little tired.  What does this mean? Should I be worried?

[ovaz129]

Did the sac measure 5 weeks when you had your 6 week ultrasound?

[mommom2]

If you haven't talked to you MD, I would definately call him ASAP, he should have some kind of after hours pager number on his office answering machine. If you need meds. you need them now.  Did the tech tell you it hadn't grown? Maybe she had it more magnified last time.