It's fine to binge a little during pregnancy -- a milkshake after lunch every now and then, an extra scoop of ice cream for dessert -- but if your diet consists mainly of high-fat, sugary snacks or fast food, you're right to be concerned. Your growing baby relies on you for all his nutritional needs, and he'll be healthier if he gets a mix of nutrients from fruits, vegetables, whole grains, and protein -- not just empty calories from the local bakery.
Cravings are a normal part of being pregnant, but try to enjoy your less-healthy favorites in moderation. Split an order of French fries with your coworker instead of going for the whole bag, for example, or try a tiny sliver of pie instead of carving up a huge slice.
If you find that you really need help controlling your cravings, ask your doctor to refer you to a registered dietitian who can help you substitute the junk food you're eating with smarter choices and create a diet plan just for you. Maybe having a professional identify why you're eating what you're eating will result in a lifestyle change that extends beyond your pregnancy. After all, you'll need all the strength and energy you can get to keep up with your newborn.