Misscarriage

Hey ladies jus turned 37 and today I would have been 8w 2d. First scan I was 5w 5d sac was 0.8), last weeks scan I would have been only 7w 4d and got told I have no baby jus sac and placenta sac had only grown 1mm in 13 days.

had betas done and hcg was 2900 (so basically in two weeks hcg only got 100 more than last time idk if it got higher between those two weeks as they didnt test again till this last scan)

My question is how long does it take for hcg to come down?

In last 5 days only came down 100 and I'm due to go into hospital tomorrow for treatment and if that doesn't work I have to get a d&c (this will be my 2nd misscarriage and 2nd d&c if I end up having to do that). Any info will be appreciated and or questions I should ask would be great as well I do plan on sending away the sac and placenta for analyzing as i would love to know why this happened.