3 hour test

I failed my glucose test my number was in the 170's and I have to go back tomorrow for the 3 hour test! I'm really frustrated because even though I have been overweight before pregnancy i have been eating healthy and going to the gym to walk on the treadmill at least 4-5 times a week! Has this happened to anyone else? What do u recommend I eat? I usually have plain yogurt with a little honey for breakfast, a salad for lunch, my snacks are usually an apple with peanut butter or banana or popcorn and dinner I usually eat chicken and quinoa ? How are my levels so high?