What you describe is something that I've been dealing with for a long time. My dh had it, as well. We are still dealing with it, but it's gotten easier.
It is a form of hypoglycemia. The problem with diagnosing hypoglycemia, is that it's a multi-causal symptom, not a disease like diabetes. Hypoglycemia can be a precursor to diabetes, as well. It's definately related to your ability to regulate your blood sugar properly.
If you have a glucose tollerance test, be aware that most doctors don't know how to evaluate the results. Giving the test is easy, if you can get a doc to administer it - it's not easy on you, because it requires so many blood samples and a crazy fluctuation in blood sugar - but the bottom line is the degree to which your blood sugar changes over each period of time, not whether it is within a specific range start to finish.
There is so much information, you may feel inundated.
Researching Syndrome X is a good resource.
but be aware that these symptoms are precursors to diabetes, not a definate path, but something to be aware of.
Also, consider researching chromium (with picolinate) as it helps your insulin regulate your blood sugar. When your pancreas gets over worked, it produces malformed insulin that has trouble attaching to your cells and moving sugar into and out of your blood and cells. When I discussed chromium with someone, they said it's been proven not to help with weight loss. That's true, it doesn't help with weight loss, specificly, it helps regulate blood sugar by supporting your insulin hormones. It also helps w/increasing muscle. But, I urge you to research it before blinding adding it into your regimine. It has helped me out a lot and I notice when I stop taking it. Picolinate is sort of a catalist that helps your body absorb it properly, any other catalist won't be as readily absorbed.
Here's a list of book reviews
on my naturopath's website. She's reviewed Atkins, Syndrome X and a bunch of other books related to nutrition, a lot about diabetes and blood sugar issues, as well.