Hypoglycemia has been called "disglycemia" "disinsulinemia" "phosphate diabetes" "blood sugar fluctuation" "unstable glycemia" "carbohydrate intolerance" "metabolic resistance"
This makes clear that when not caused by organic problems (insulinoma, hypotalamic tumor, renal glycopenia and others) it is caused by a faulty sugar metabolism.
That's why it so hard to detect, diagnose and find out. A metabolism is a series of functions not a specific organ or place in the body. If a metabolism is impaired it doesn't mean that the organs implied in that that metabolism are impaired as well. Which is like saying that there might be a black out in your livingroom electricity conduction even though both the switch and the bulb are perfectly intact and fine.
You should ask a 6 hours glucose tolerance test. Remember that for five days or so before the test you should consume an high carbohydrate diet.
If the test is positive and you react with absolute or relative hypoglycemia after metabolizing glucose, you have Reactive Hypoglycemia.
Reactive Hypoglycemia basically rules out the other conditions because it can be seen that you're precisely reacting to what you're eating and not randomly releasin insulin or having a deficiency of glycogen.
You may want also to check your hemoglobin glycosilated, your insulin and your epinephrin levels as well as you adrenal secretions.