"I am following diabetic diet..."
Not if your postprandial is in the 300's along with an A1c of 8.5%, which, by the way, equates to a daily glucose level of 225 mg/dl. A lifestyle change is in order. You can start by lowering your cab intake; avoiding eating white foods - white bread, white rice, potatoes, pasta and starches as the sugar in these foods are absorbed quickly after eating. Read up on the GI [Glycemic Index]. Exercise after eating not before.
I agree with ku111. Your A1C is high. My Doctor told me (Type II) that I needed to get my A1C under 7.0. I am currently at 6.5 and with my weight loss, he is slowly cutting me back from medications.
Best of Luck
Hopefully you are seeing an Endocrinologist. A1C of 8.5 is high and they need to start trying some different things for you. We have a lot to do in life and it is so important we take care of ourselves. Goodluck!