Hcg rise and drop !!

Hi , anyone have any idea why hcg drops and rise again? I had hcg level of 850 when I was. 5wks 2 days then it dropped to 200 when I was 5 wk 5 days now it started increasing again and reached to 1200 ? When doctor saw hcg drop she told I am miscarying , but m confused now that whether I should keep any hope or not ?