Hi Maudie
Not sure what the statistic is, but I know plenty of people who have had it happen.
They've had to go for an early scan for dating purposes, as they haven't had a full cycle before getting pg.
But I think it's fairly common, as your body is still awash with hormones.
However, you'll want to get a blood test done at the doctor, rather than relying on a POAS test, as you may still have some residual HCG in your system, so it may be confused. So a POAS may say positive, but you may not be pg. IYKWIM?
Good luck