Positive Test and Blood - No Pregnancy

I had these positive tests yesterday at different times of the day but I only had a period 2 weeks ago and we only dtd 5 days ago for the first time this cycle.

I thought this was odd so I contacted my gp and she referred me for a scan. As suspected, there was no sign of a pregnancy on my scan but blood levels came back at 653. I’ve got to go back in 48 hours for repeat bloods but I can’t see how I can be pregnant, implanted and positive test within 5 days. It’s literally impossible.

The period I had 2 weeks ago was definitely af and not implantation and even if I’m wrong on that, it would be make me nearly 7 weeks pregnant and they would have seen something on the scan today surely.

Has anybody ever had a false positive or could suggest what could be causing this. I’m loosing my mind