Worried about miscarrage

I had a miscarriage in June with an HCG of 200 that only jumped 25 points in 3 days... we just found out that we are pregnant again. I requested a Beta and just got the results back this morning. They said that I am at 476.7. They are going to do it again on Friday and I know that we need to hope for the double. I am just looking for a glimmer of hope here. I am having lower back pain.. no bleeding. I missed my period 6 days ago.. although they say that i am 5 weeks pregnant.. (because of the BetaHCG).. Just looking for some explanations and some reassurance... We have 2 healthy boys now and want so desperately:angel: to have another. I am so worried about losing this one.