Hcg more than tripled, then 2 days later dropped by 10....

A week and a half ago on sunday, i got a faint positive pregnancy test, then another faint positive tuesday. Then started bleeding like a period wednesday and thursday so i thought maybe the faint positives were false. took a test the next day on friday and it was clearly positive. Went to ER on saturday and blood hcg was 49 and monday the hcg jumped to 163 (more than tripled) then just had another test done yesterday (wednesday) and instead of at least doubling, it dropped by 10, making the hcg 153..... Doctor thinks it is a miscarriage but i was wondering if anyone had their hcg drop by jist a little and still had a viable pregnancy???