Beta hcg low but doubling

Anyone experience this? I thought/think I am about 6 weeks along but I definitely ovulated a couple days late this past month and am thinking I might have implanted late as well now too... Beta hcg results came back at 229 beginning of 5 weeks and 710 72 hours later (more than tripling). Doc is happy with the increase rate but the numbers themselves are low. Anyone out there go through something similar?  When I mc'd at 10 wks in September my level was 82000 and then went down to 69000 so I know high numbers aren't everything... Just looking for some reassurance! ?