Drop in HCG

On the 08/24 I went to the doctors and got bloodwork , I found out I was 4 weeks and a few days . My HCG levels were 1900 . I’m now 5 weeks and today 08/27 and my HCG levels drastically dropped to 176 . I finished implantation bleeding the morning I got tested (got tested in the afternoon) . The implantation bleeding was light light pink and only showed every few times I peed , it only got on my panty liner the first 2 hours it started . Anyone know what may have caused my HCG levels to drop ?? Will I still be able to continue pregnancy ?? I already had one miscarriage a year ago in September ... Doctor is seeing me tomorrow . I feel fine , nothing hurts , still experiencing the same symptoms I was before (nausea , tender breasts , fatigue) .