Hcg level HELP

Ok, so last week on Thursday I found out I was pregnant. Friday I started spotting, and gradually over the weekend it turned to heavy bleeding and lots of clots. Monday I had a beta hcg done, and it was a 22. My dr said he believes I’m miscarrying and to come back in a week for another hcg test and to discuss what do do next.

So why am I still getting pretty positive tests?? Surely with a level of only 22, my tests should be at the very least getting lighter, right?? I’m like 16 dpo today.... How long would it take for a 22 to go back to zero??

Any experience/knowledge you have is appreciated. Thank you.