Question about my hCG following a cp

On the 9th of this month I found out I was having a miscarriage at four weeks pregnant, on that day a blood test showed my levels being 50. The following Tuesday, the 12th, my levels were 17. Following that shouldn’t my levels be either zero, or so low that they would be undetectable on a regular home test? Well yesterday, so a week and a day after my levels were 17, I took a first response test because of some nausea that has started coming back, i wanted to make sure, and within 30 seconds it came back obviously positive with a line almost as dark as the one i took on the day my levels had been 120. Is this normal, should I be worried? I have a app this afternoon to check my levels again but im trying so hard not to have hope that maybe they were wrong and my baby is okay, even though i know its not. And it doesn’t seem possible to be pregnant again and already having a positive test a week after a cp. any advice or help? Thank you!