My husband had BG levels of 400 for months and now feels dizzy and nauseated with BG in the 250 range... any advice

I don't understand doctors that don't test blood sugar. And I'm also upset that doctors just tell you something like, "It looks like you have diabetes, let's try this pill and we'll check again sometime", treating it like it's no big deal. It IS a big deal. Diabetes is a devastating disease, and having it is emotionally depressing.

I have to tell you that 250 is too high (unless you're testing right after a meal, I guess, which is the wrong time to test). Two hours after starting a meal is one recommended time to test, and you want it to be under 180. Other times are in the morning after a 12 hour fast, you want it no more than 120 max (which is pre-diabetic, it really should be under 100 to be healthy), and before meals and bedtime under 120 or so. 

You MUST do more about this disease than your doctor is doing.  Look on the internet for the phone number for maybe the American Diabetes Association, see if you can get into a diabetes teaching group in your area. Get informed with good sound medical advice, and avoid listening to anyone with miracle cures.  Schedule an appointment with a nutritionist or dietitian (I'm not sure what the difference is).

Get a good, up to date book about diabetes. You have a lot to learn.

I pray that there isn't any permanent damage that's been done, and I wish you all the best.

And think about getting a new doctor. Seriously.