When you say the reading is 150, is that your fasting level taken first thing in the morning?
When you do your first reading in the morning, aka fasting reading, it should be under 120. So 150 is high, but it's not extreme. Worrying and stress will make it worse. Also, remember that your doctor is letting you control it naturally and not putting you on medication. That's excellent! Try not to stress or "freak out", it'll be just fine.
Most women control GD by diet and exercise. You just need to make a few adjustments to your lifestyle. Try eating 6 times a day, about every 3 hours (light breakfast, morning snack, small lunch, afternoon snack, small dinner, evening snack)
In addition, to the advice given by your doctor, here are a few more.....
No fruit juice
I would limit the amount of milk
Drink water, water, and more water, go pee, and drink some more water
For beverages herbal or decaf tea, seltzer, add a lime or lemon slice to your water or seltzer
Limit carbohydrates - very little potatoes and rice or avoid altogether, also limit bread and avoid white bread
Eat lots of green veggies (remember corn and potatoes are not considered veggies on the diabetic diet, they're carbs), orange and red veggies are good too, but limit them
Read labels, check cereals and condiments for sugar content
No chips or packaged snacks. Low fat, high fiber crackers are good.
Yogurt - you can have the light variety
Some meal/snack ideas...
Oatmeal with raisins or apples, use cinamon to flavor
1/2 whole wheat bagel with cream cheese and a piece of fruit
stir fry - lean meat with a variety of veggies (onions, carrots, celery, green pepper, snow peas, broccoli) with a small portion of rice
low fat crackers with low fat peanut butter
sugar free jello
sugar free jello pudding made with 2% milk
large salad, add some grilled chicken breast
taco's - meat w/onions, lettuce, black beans, tomatoes, a little bit of cheese
whole grain crackers w/humus
raw veggies with dip or humus
omelette - add lots of veggies (mushrooms, green peppers, onions, tomatoes), keep cheese to a minimum
Please don't worry. There's really not much to worry about. Both you and baby will be just fine.