Urine sticks tend not to register over time you’d be better getting the free blood ketones tester meter careens sens duo from spirit healthcare
http://spirit-healthcare.co.uk/product/caresens-dual-blood-glucose-and-ketone-meter/
It comes with two free strips but any more cost 10 pounds for a pack of 10 with free delivery - but you don’t need to test very often. You can also use this meter to test your bgs too or not as you choose.
I now don’t register any ketones on ketostix after nearly 10 months on keto but on my meter I register at least 1.6 most days when check which I do about once a week. I find it reassuring.
Gather you can buy something to test ketones with Libre but don’t know anything about Libre as never used it.
Good luck you are probably still in ketosis it’s just you don’t spill ketones into your urine when you are an adapted fat burner!