A blood sugar of 400 is extremely high even immediately after a meal!!!! I would find another doctor immediately!!! I do not understand why you haven't been put on meds already...an Endo as suggested above is a great idea and start reading everything you can about Diabetes...doctors can only teach so much, it is up to you to educate yourself and learn to be an advocate for your own health...please start today!! Good Luck... ;)
Well, one question I would have is at what time was the sugar level taken? A reading of 400 immediately after eating is one thing. The same reading two hours later is another.
It appears you are a candidate for medications.
You really need to see a diabetic specialist and take a test known as the A1C.
It doesn't sound like you have a very good doctor. Four hundred is WAY too high (200 is too high!). What did your doctor give you for target range? What changes did he ask you to make in diet and exercise and weight? Did you get referred to a diabetic educator? If you have done these things and are seeing numbers like that your diabetes is very out of control and you do need meds. My suggestion would be to get referred to an endocrinologist who is a specialist in diabetes and get on the regimen of diet, exercise, weight loss and medication that is going to get those numbers in control.