hcg rising but not doubling.

Hello ladies, I have had 2 previous misscarriges I am expecting again. I am currently 4weeks 3 days. I had my first hcg drawn at 3week 5 days it was 64 at 4week it was 164 and at 4week 2 days it was 266. it did double the first time but did not double 2nd time I worried I might miscarry again. Has any one gone through same situation and had successfull preagnancy?