Glucose tolerance test, preferably a 4 hr one.
This would show lows, at the 3-4 hr mark. Shorter tests do not.
Doctors often use a 2hr, which will not typically reveal hypoglycemia. The 2 hr only shows highs for diabetics.

HbA1C shows if your diet is high in carbs and you are having spikes after eating. It is an average of long term sugar utilization.

Fasting glucose is done to screen for pre-diabetes and diabetes.
In people with impaired glucose utilization, it may show lows at first and as years pass then it creeps up slowly to over 100.
This process is also called insulin resistance.

If you have had periods of remission of symptoms, then definitely something is causing that, and diet is the most common cause. So if you clean up your diet, you may see improvements. They will be slow but will sustain, if that is your issue.