How many calories are you trying to eat? It can be hard to manage with fast food, which really is meant to be as bad for you as possible. It might help to have a supply of snacks like protein bars, nuts, etc. in the car or such you can fill up on so you can get something very small if you have no choice but to eat fast food. Even at someplace really gross like McDonald's (if you must!) you could get a double cheeseburger for about 450 calories. Combine that with a Diet Coke or unsweetened tea, skip the fries, and that's not so bad. Remember that somebody your age needs around 1800 calories a day, too.

Of course, I'm staying at around 2300 right now, just in a slight caloric deficit and going to the gym 4 or 5 times a week. Thank you for the suggestion though.