High HCG after a Miscarriage

I’M SO CONFUSED. Has anyone experienced this before?

Found out I was pregnant on the 14/12/22. Started spotting 3 days after. Thought it was normal. Had severe cramps and started bleeding heavily on the 19th. Went to EPAU did a scan and they couldn’t really see anything as I was only 4 weeks and 4 days. Bled for 7 days with clots and tissues. Went back and they did a vaginal Scan which shows there was nothing in my womb and that I had “miscarried” this was on the 23rd of Dec. They did a blood test same day and asked me to come back on the 26th.

Blood test on the 23/12/22 HCG was 38

Blood test on 26/12/22 HCG was 66

Blood test today 28/12/22 HCG 88.

I don’t understand. why is my HCG increasing if they thought I had miscarried? They want me to come back in a week and if it’s still high then they will do a scan. This is stressful. Don’t wanna keep my hopes up 🥹🙏🏾