Heya, I hate hcg levels!! Hahaha they send me crazy with worry but only cos I have been there recently as well. Anyway I think they look fine given the 6000+ 'rule'. Mine doubled like crazy as yours did until about 11000 from memory and then took 3-4 days to double from there. My GP was worried as we had had two previous losses so set us for a dating scan straight away. I was only 6w3d as expected (by ovulation - by af dates I would have been over 7 weeks) which explained the levels and yes she agreed after 6000 they can slow down. What was the results of your ultrasound??
Everything crossed for you!!