HCG rose quickly, now tapering off

Hi,

My HCG has gone from 44 on July 9 to 6,846 on July 28th.  Over the past four days it's only increased to 7,723.  When I went in for my first u/s they only saw a gestational sac.  I go back on Monday for another ultrasound, but they said this small of HCG increase is worrisome.  Also, they said I look more like 4/5 weeks at my ultrasound, not the 7 weeks I thought I may have been.

Please let me know your thoughts of what you truly believe are my chances.

Thank you.