Fluctuating hcg after miscarriage??

I miscarried just over two weeks ago at what would have been 5 weeks. I did have an ultrasound right before due to spotting that showed a gestational sac.

Bleeding started 11/2 and lasted a week, no large clots, but it was an early loss. Did a follow up ultrasound and blood draw 11/13 and the inconclusive results are stressing me out. It looked like there was still a sac there. It also looked like there was maybe a cyst (which had been possibly identified at the first ultrasound) but it had grown and had what looked like a dividing wall in it. Hcg was down from 700 to 300 in a week and a half, which seemed really slow.

I’ve been taking pregnancy tests to check on things and they’ve been veryyy slowly dropping, but then today 11/17 the test was darker than the previous ones. It’s only been just over 2 weeks since bleeding started so there’s no way it can be a new pregnancy, right? Can retained tissue cause hcg that has fallen to rise again? I’ve had unexplained nausea too. I’m waiting for the date of another ultrasound to get a better look at things but my mind is spinning in the meantime and the illogical side of me wants there to be a viable pregnancy :(