Not silly. Our levels fluctuate throughout the day. The things that affect levels are many, including: excercise, food, stress, fatigue, infection as well as liver dump. A difference of 1.5 should not concern you as it is a fairly usual occurence.
There are many things which can affect your BG.
A couple of things which I can think of are work related - exercise (if you have a very active job) and stress definitely affect your BG.