pregnancy hcg question?

Im so confused. Ok heres my story. My last period was July 1st. Aug 2nd my HCG levels were 98, Aug 4th they were 283, Aug 11th they were 3,321. So on Monday Aug. 18th I had an ultrasound and the tech said he saw a sac and yolk but no fetal pole, this morning my dr called and said he thinks Im having a miscarriage after reviewing my Ultrasound, since there was no fetal pole at 6 weeks, he sent me this afternoon and had blood drawn again. He just called back said my levels were 11,000 and he was very happy with that. I told him i thought numers were suppose to double he said no not everyones double and alot of time when they reach 10,000 they slow down. He says he now thinks I have a normal pregnancy and to go in for another ultrasound tomorrow. I know 11,000 is a low HCG but he said not to pay attetion to the numbers, has anyone had a succesful pregnancy with a situation like mine?