I just wanted to pop my head in and say something.
HCG testing is a great way to monitor the progress of a pregnancy, but don't get too worked up if the results aren't what you expect. As Melinda said, it doesn't always double in 48 hours, as long as it's rising that's what counts.
My hcg was taking 5 days to double with this pregnancy. We stopped monitoring it after a couple of weeks as it was stressing me out too much and early scans were all good.
Every pregnancy is different and as you can see from my ticker, the slow rise was not a problem in my case.