It can take up to a month for metformin to kick-in fully.
You don't define what you mean by good eating- but your numbers are influenced by the number and type of carbs you are eating, and your sensitivity to those carbs. There's plenty of posts in the archive that describe Jeannie's - nothing white but cauliflower diet, the Insulin-resistance diet, Dr. Berrnstein's diet, and the Atkins diet.
You might want to check these out and see how your current eating plan compares. Generally speaking, when you drop your carbs, you drop your numbers- Your challenge is finding the carb level that nourishes your body AND keeps your sugar at an acceptable level.
Exercise is a powerful way to drop your sugar level and keep it there. I work out for an hour every day- simple stuff- walking, biking, chair-dancing. If my sugar is high, I can drive it down 20-30 points simply by vacuuming my house for 20 minutes, or mopping my floors to my favorite Bob Seegar or Jimmy Buffett CD.
Losing weight, if you need to- is even more powerful.
If you rely on metformin or any other drug to regulate your sugar- you'll be disappointed, and on multiple drugs before you know it.
When I was diagnosed 15 months ago, my fasting was 457 and my A1c was 15. For the past 9 months, my A1c has been around 5.0 and my 30 day average is 92- you can get your sugar under control- it'll take work- but it will happen. Good luck!
sandy