My fasting BG does this.
I wake up at say, 6.1 trundle around showering, dressing, wallpapering the facial cracks, and by the time I sit down to brekkie, I can be anywhere from 6.8 to 8.5
It kind of makes a mockery of the doctor using my fasting BG as a diagnostic tool.
Over the last year I have been trying to work out why, and I've discovered that in my case, the following have a big impact:
Amount of sleep (sleep deprivation drives it up)
Level of background stress (the more stress, the higher it goes)
Level of stress that morning (a job interview would send it sky high!)
Food the night before (carbs drive it down in the morning, but increases my max BG levels for a day or two)
Exercise levels, both short and longterm (regular exercise reduces my BG levels overall)
Exercise that morning (extra trips up and down stairs before breakfast cause it to rise a lot)
Extent of low carbing (reduces my overall BG levels delightfully)
What time I eat breakfast (the later I eat, the higher it goes)
So now, I have a low carb snack before bed.
Then a Brazil nut before I get out of bed (usually stops the rise)
I try not to do anything physically demanding before breakfast
And I eat breakfast as early as possible.
Your mileage will
of course vary