HELP ME

Long story short. I got a bunch of positive frer and digital from the 16th - still today. On the 18th i started heavy bleeding. this lasted until yesterday. I went to the ER a few days ago they said my hcg level was 7 and that there was nothing on the ultrasound. I would have been 3 weeks 6 days at the time of the ultrasound. my tests are still really positive. Has this happened to anyone else?? if my hgc was 7 on the 20th wouldn’t it be way gone by now? could i possibly still be pregnant?