What can I expect for hCG doubling #s, and is mine too low?

I just found out 2 days ago that I am pregnant. We weren't trying, but I was aware there was a possibility so I tested early. Anyway, I have a history of one miscarriage at 10-1/2 weeks and also have a 16-month-old daughter. This being my 3rd pregnancy, I'm cautiously optimistic. Still, to ease my mind I went in for my first hCG draw today which was 45. I'm apparently 13DPO according to dates. Is this too low? I know that there is a very large spread for normal numbers, but I need to hear from someone who had this type of number and ended up with a healthy pregnancy. I will be going back in 1 week, and I am also wondering what I should expect for a good number. I would be 4 weeks 5 days with an hCG of 45 at 3 weeks 5 days.