HCG levels at 4 weeks

Hello! I had my HCG levels drawn at 14dpo (4w3d pregnant) and they were 85. This was last Wednesday. Had them drawn again yesterday and just got a call that they were 1498. Going back in tomorrow for one last redraw. Nurse said they are doubling fast. Should I be concerned about that? Or is that a good sign? I was always told the normal doubling rate was 48-72 hours, but based on the doubling calculator my rate is approximately 27 hours. Thanks in advance!