no sac 4 weeks 5 days pregnant

Hope

I've had some mild cramping, but more cramping on my left side than right. I called my dr and they said since I was not an established patient they couldn't see me until 8 week. I went to the ed had a 600 hcg level (normal), but no sac visible in uterus. which is also normal, but could also be a sign of miscarriage. I have had an ectopic pregnancy and tubal removal so I am nervous. anyone else have these things happen and have a normal pregnancy?