In my own personal experience, the Metformin will do very little to change your blood sugars if you are still overweight and eating loads of carbs, drinking sugary drinks etc. I've gone far too long not changing my diet. I tried, but I followed the advice to eat balanced meals and still stacked up on carbs and then craved more carbs.
Since I've found this site and seen how others have used a low carb diet to control their blood sugar I've changed my diet. I'm eating low carbs and lower calories than before, yet I've not been feeling hungry or wanting to grab anything and stuff it in my mouth. Consequently, my blood sugar has come down from your kind of levels into 'normal' levels - all in a month.
I'm not saying this would be the case for you, but if you are overweight and you eat lots of carbs that's where you need to start IMO.