rising hcg after miscarriage

[user1476971714]

Hi, not sure if anyone can shed any light and i apologise in advance for my confusing post... On September 30th i had a miscarriage at 6 weeks - back pain and bleeding for a few days and not heavier than a period. On 4th October hospital confirmed miscarriage and said that my pregnancy test was negative and sent me home with leaflets. On the 7th October i felt rough and HPT was showing positive so went back to early pregnancy unit who did HCG tests with a result of 194 - told me to test again in 2 weeks time but 6 days later i still felt unwell so asked for another HCG blood test with came back at 480 - they scanned me as suspected ectopic but found no sympyoms so recommended another HCG test 48 hours later - came back at 670 and was told it was bad news. I was booked in for a further 2 days later and was prepped for ectopic treatment as HCG came back at 813 - not the doubling it should but they decided to scan before deciding treatment. The internal scan showed a small sac which they said looked like a very early pregnancy and a small bleed next to the sac - because of this they would hold off any immediate treatment for ectopic until they scan me again in 10 days time. The hospital have said its not a textbook case and the short answer is 'they dont know' which of course doesnt help my worrying. A potential twin pregnancy where one has not develpoed has been mentioned as a reason for the HCG not doubling - has anyone else been in this situation? I'm not getting my hopes up as i know the likely answer is an ectopic but there is a small chance of a viable pregnancy. Thank you.