It could be illness. Even a minor cold can raise glucose levels. It could be time of the month. It could be you had something sugary on your fingers.

But, FWIW, my glucose goes up overnight. I can see the post-dinner spike, have it end, go to sleep, and when I wake, my glucose is higher than when I went to bed. What it is when I go to sleep has only a little noticeable impact. (I have seen an impact from exercise, though.)

If your fastings are consistently above 100 (or some people say 110), it may be worth consulting a doctor, as some doctors might elect to prescribe metformin for you.