I am glad that you are following your doctors and nutritionists advice on diabetic diet. You obviously are giving yourself insulin based on the carb count. That should keep your sugars under tight control. But too many carbohydrate and insulin will eventually lead to excessive weight gain. Be careful of how much weight you gain.
Diet drinks are okay but please drink them rarely. Water is the safest drink (no calories, no artificial sweeteners). You may use a touch of lemon in it to make it taste better.
Wish you all the best with this pregnancy. Remember to monitor your sugars after the baby is born. Some women develop diabetes after being gestational diabetics.