6 weeks low hcg 😓

I have had 1 miscarriage already this year. When I got pregnant again my doctor wanted me to get labs early to see if this will be a viable pregnancy. She said if the Hcg doubles within 48 hours then it's a good sign. My Hcg is going up but not doubled and she says it is low for how far along I am. I don't remember the exact number but I had them drawn at 5 weeks 5 days and it was in the 400s (up from low 300s 2 days prior) 😓 The doctor is having me do an ultrasound on Wednesday to rule out ectopic pregnancy and is concerned that if it's not that there is a good chance this could be another miscarriage situation 😭 I'm wondering if there is anyone else who has gone through this situation? Has anyone had low Hcg levels around 5-6 weeks and then had the pregnancy progress alright? I'm just really trying to stay positive.