Should I take metformin if I'm in control of my Type 2 diabetes?

I am in complete control of my Type 2 diabetes. My A1C is 5.0 and my fasting blood sugar range from 73 to 90 and before I sleep, it's around 77 to 85. I eat 5 to 6 times daily and most of my carbohydrates comes from fruits and vegetables. The highest I seen my blood glucose in the last 3 months is 120. I exercised about 1 hour a day. My Doctor still want me to take 1 tablet of metformin 500mg 3 times per day. I am worried because sometimes by blood sugar is at 73. What will be the effect if I continue taking all that pills? For the last 3 weeks, I am only taking between 250mg to 750mg of metformin and my blood sugar is in control. Please advise.