gestational diabetes?

Lindsey
So I'm currently 15 weeks today. 2 days ago my doc had me take the glucose test as a precaution cause I'm slightly over weight and my last baby (#3) was born weighing 8lbs 13oz! Today the doc called and I failed the test. I have to go back in on the 15th to have the 3hr test done. 
I'm thankful they are testing early just in case I do have GD. And I've heard story's where people that failed the 1hr pass the 3hr test. I'm just wondering if any of you have had GD? And what do you have to do to help the situation? I've heard diet, exercise, and sometimes shots. My diet is pretty good I don't eat much sugar or carbs. And I exercise regularly. Guess I'm just looking for any thoughts and input. Thanks!