miscarriage but rising HGC

This is my second miscarriage. After a loss in November at 10 weeks I found out I was pregnant again Wednesday last week. I had been bleeding heavy for two days and spotting for eight more days before I took a test, I first thought I had a weird period after the last miscarriage. When I got a positive I called my doctor and he told me to come in the next day.
I went to the appointment and he couldn’t see anything on the ultrasound (vaginal), he told me to get blood drawn Saturday and Monday and come back today for another ultrasound. Saturday HGC was 425 and Monday 692. I was slightly positive because even though the numbers were low and didn’t double they were rising, but today again he couldn’t see anything on the ultrasound and told me I must have miscarried.
Now, a few hours after, I’m starting to have doubts. Yes, at this point he should have been able to see at least a sac (based on last time I had sex even with very late ovulation and implantation I would be min 6 weeks), but why do the numbers go up? The last time I had even a drop of blood was last Friday, both blood tests have been taken after! I’m just really confused and I still feel pregnant 😢
Edit: he did check for an ectopic, but couldn’t find anything besides 3 cysts (that he didn’t mention last week). He just told me to handle it as if I’ve had miscarried and to come back in 3 weeks for another blood draw and u/s to make sure everything is out. I used to love my OB, he delivered my daughter 9 month ago and was awesome, but now I feel like he doesn’t take my concerns seriously... how am I supposed to wait 3 weeks not knowing?!?