Hcg not doubling but baby is growing?

Natalie • Mama of two little boys and a baby girl due October 2019

I had my hcg drawn at 6 + 1 and my levels were 4100 and 48hrs later they were only 5100 so they didn’t double. I had a scan at 6 + 1 and the baby measured perfect with a heartbeat of 113 and then another scan at 7 + 1 and the baby still measured on track with a heartbeat of 137. I have not had my hcg retested since but I’m still concerned. My midwife thinks it’s unusual that my hcg didn’t double but she still isn’t worried. I guess I’m just looking for some re-assurance or similar experience from someone else. I’ve had 2 miscarriages so I’m freaking out...