I can't add anything except for more information.
We can't diagnose but we can give advice about how to treat and control the conditions.
I was exactly the same, I was ill, I kept falling asleep, knackered, I didn't have a clue, nor did my doctors, I was putting on a lot of weight. They kept saying it was my misdiagnosed T2. My Hba1c was normal, my fasting was normal. It was only post prandial when something happened. The symptoms were really bad.
I was constantly going hypo.
The reason why? I produce too much insulin, as a secondary insulin response to the quick spike. This excess insulin is what puts me into hypo.
For me, it was the carbs, I'm carb intolerant and my condition is called' Late Reactive Hypoglycaemia'!
However, it is possible to control the condition by discovering how certain foods affect you.
You need an endocrinologist who has had experience with rare metabolic conditions like my condition. And yes it is quite rare. This is why your GP doesn't have a clue. And because of this, you need a referral to a specialist endocrinologist. So the diagnostic tests can be done.
Keep safe, keep asking, let us know how you get on.