What Causes Persistence Light Headedness?

I am on Lantus for about a month now. Since then I have started feeling light headedness continuously. Initially it was very severe. Now it has reduced, but still persists. I am also taking Glimepiride (80 mg)+Metformin (500mg) in the morning and Metformin 500 mg sustained release at night along with lantus. I am feeling this lightheadedness even while typing this message. Kindly advice.