If you do plan on eating healthy, it's best to keep foods such as ice cream, pop, etc out of your diet as much as possible, even if you're having a good week. Those kinds of fats and sugars are not beneficial and there are other good tasting foods that can make you feel more full and offer more nutritional value. When you do have a "good week" continue rewarding your body with healthy food. There has been a link between unhealthy foods and physical addictions to them.
With that being said, I try to eat healthy and avoid unhealthy as much as possible. If I crave something sweet, salty, etc. I try to find a healthy food that will satiate my craving without sacrificing good eating habits.
And there is no need to eat huge portions! You're not doing your body any good by over eating. Five to six small meals a day will help keep hunger at bay and help your metabolism functioning at a good level.
I'm also somewhat of a gym rat, so I exercise almost everyday. There's nothing wrong with a little sweat!