May do. The effect on blood glucose seems to vary from person to person. It is not a medication that we would normally avoid in diabetics. In fact it is the first line (most strongly recommended) treatment for nerve-related damage in diabetes. If you are finding your sugars are higher than expected you should review it with your prescribing Dr.
500mg? Is a little high. Did you mean 50mg? Yes it is listed as a side effect on the nz medsafe data sheet but may not be a trivial decision to stop/reduce depending on what it is treating. Best to discuss with your GP who will have a better idea of your overall record .
Not directly. It will affect metabolism of other drugs and can cause weight gain but should not affect the actual reading directly.