I get periods of unexplained excellent blood sugars , they can last up to a week or so for me. I put it down to the body being more sensitive to insulin during this period , I couldn't correlate it to anything else.
Have you upped your exercise regime? I sometimes find vigorous exercise (e.g. ~ 10 km run , ~20 mins rowing and ~30 km fast cycle in the same day) gives me perfect blood sugars for around 3 days after. By perfect/excellent blood sugars I mean non-diabetic levels ~ 4.6 mmol.