Your fasting blood sugar is still within normal range, so I wouldn't worry too much about it at this point. Just continue to keep an eye on it. Diabetes is diagnosed solely based upon numbers, meaning that diabetes and pre-diabetes are the same disease process and just one blood sugar point can differentiate the two. Diagnosis requires 3 separate fasting blood glucose tests, spaced apart. A lot of things can affect your readings, aside from just diet- exercise, hydration, stress, illness, etc. I would just continue to lead a healthy lifestyle. Keep an eye on it, but don't obsess over it. There are a lot of variables, many of which even the doctors can't always explain. If you're concerned, you can google the glucose reading criteria for diabetes and pre-diabetes.
Sorry, title should be Blood sugar has months of being slightly elevated then goes down. I can't edit the title.