Since the level of BG needed to DX diabetes is arbitrary and has been going down over the years many believe there is no difference between pre-diabetes and diabetes.
yes, stress can raise BG... however a non diabetic would not have high BG even under stress.
So your BG control system is not 100%
Have you done a hba1c test? This test gives an average 3 month blood sugar level. Normal level is less than 5.0. Suggest you get this test done as soon as possible.
Your doctor is wrong to refuse to treat you. Untreated prediabetes always progresses to diabetes. It is easier treated earlier than later. And complications will collect.
Suggest you get your own meter and test what is happening 2 hours after eating. Normal should be less than 120.
Test fasting every day, or every second day to get a better picture.
You could also look into changing your eating habits. Type 2 diabetes often responds very well to restricting carbohydrates / adopting a low carb or ketogenic type eating approach.
Exercise and normalizing body weight, if overweight, are also beneficial.