HCG Levels

Wondering if anyone has had their level tested in the very early stages of pregnancy (possibly right after implantation and + pg test) and results been very low then more than double 48 hours later despite low number but still in "normal" range? Early pregnancy here after two MMC and I tested + very early, not sure on dates because I conceived after the second cycle after D&C and my first HCG was 11 (very faint positive) and two days later it was 64. Again not sure how far along I was. I am waiting for another HCG tomorrow after a week and I'm hoping and praying it's a good normal range number. Anyone had low numbers at first and gone on to have a healthy pregnancy.. my numbers started off low last pg I lost it so I'm worried sick. Thank you and sorry for the long post.