First off, this "prediabetic" range is a new development. Just a few years ago fasting "normal" was defined as <110. So you are very close to the old normal.
The effect of diuretics on blood glucose is a well documented but very small effect. In any case, it probably isn't affecting your march toward diabetes because blood glucose is an EFFECT rather than a CAUSE. An analogy: melanoma gives you black spots on the body but painting black spots on your skin won't increase your risk of melanoma.

(I LOVE analogies

)
If you indeed are progressing to Type-2 diabetes, which I doubt, then more might be gained from losing weight and eliminating sugars.
Norvasc MIGHT be enough, but don't count on it; the diazide is the better antihypertensive.