Gestational Sac with No Heartbeat: Early Pregnancy Concerns & What to Expect

Question
good day! i am 30 years old i have 3 little boys all had first trimester bleeding one was diagnosed as subchorionic hemorrage all went to full term.  i am now in my 4th pregnancy.  i thought i was about 6 weeks along.  went to the ER the other night due to shrp stabbing pain in my right abdomin plus a bit of red spotting.  they could not find the source of my pain but did find a gestational sac, no baby no heartbeat.  they said it was to early to see that.  then diagniosed me as being 5 weeks not 6.  here is where i am confused.  my period was August 18th.  I ovulated on Sept. 8 or 10  It is now October 10th  according to my last period i will be 7 weeks almost 8. (gestational) according to my ovulation date i should be about 4 weeks (fetal age)   neither one of those dates seem right with the sono results. I am ssuming when he said 5 weeks he meant 5 weeks gestational and not fetal age.  that would have put my conception a week later and that just is not possible considering we hadn't had relations since the 10 th of September again this is the 10th of October.   are you confused yet?  not only that they found a subchorionic hemoorrage with this one as well.  so is it just to early to see anything what's up with the dates?  how far along am i really?  
sept 20 hcg level 24
sept 23 hcg level 111
sept 27 hcg level 647
October 9 hcg level 12,634
i think the hcg level is pretty good but. seems pretty high for a 5 week pregnancy.  so all i want to know am i further along than five weeks but something is wrong no baby, blighted ovum, chemical pregnancy etc or am i five weeks and you think i will see the yolk sack in a week or two?  they said nothing about a follow up sono.  btw it was abdomianl sono not transvagianl.
can you shed some light on this big mix-up of mine.  thank you so very much for your time!
michelle

Answer
Your HCG values are wonderful and indicate a viable pregnancy. A sonogram taken at 5-6 weeks will only show an empty gestational sac, and will not show a fetus or a fetal heartbeat until 6-7 weeks gestational age. If your period started on August 18, you probably conceived around September 1 (not the 8th), and you should now be around 7-8 weeks, as you said. Either the sonogram was inaccurate or you are wrong with your dates. If you really are only 5-6 weeks gestational age, then you must have conceived around September 20. I would suggest that you repeat the sonogram in 2 weeks. Remember, sonograms are not very accurate at this time. The best time to take a sonogram is at 16-20 weeks from the first day of your last period. As long as the HCG values are rising, do not worry.