How quickly should HCG drop post chemical pregnancy?

 I went in today for a follow up lab and ultrasound. My highest HCG on Friday was 324. Today it only dropped to 245 (5 days later). I've had bleeding for over a week, but no pain. Today's ultrasound showed what they thought was an ectopic pregnancy. However, since my labs didn't increase they are no longer concerned. We can't start our FET until my HCG levels drop below 5. I'm just wondering how long it took everyone?   I feel like for all the bleeding I've had I would have thought my labs would have plummeted. Should I still be concerned for a possible ectopic pregnancy?