Diet and Natural Weightloss

OK i just want to start out by saying that i am one of you! i Work out 6 days a week, lift weights, cardio, run ect. ect. I eat really healthy, leans meats, whey, non-fat yogurt, fish, shrimp, canned veggies, canned fruit(college student…fresh is too expensive), oatmeal… i pretty much stay away from packaged foods (except the canned but i always get organic or low-sodium/light syrup)
my question is i tend to cheat alot, i go a week eating really healthy and excercising them sometimes i just pig out. I need a stopper and i love ice cream, especially the ben and jerrys, so here is my question, if i eat really healthy around 1500 calories a day, excercise and eat a whole container of ben and jerrys on once a week (on average about 1000 calories a container) will this be harmful to weightloss, and when i get my system flushed out will it just make it crappy again?
I need to add, i have muscles and can almost see a 6-pack, but i have a little flab around the belly, thighs and buttox, and i need(well dont need but want to) to lose the fat in 2 months for springbreak, ive been working out about 2 hours a-day, running around 3 miles. will i still lose weight if i eat one thing of ben and jerrys once a week.

I am currently doing a weightloss competition, where as though I need to lose at least 3 pounds a each week to stay in the competion (similar to the biggest loser show) im eating oatmeal and whole grain english muffin w/natural peanut butter for breakfast, to small snacks per day, and for lunch and dinner I eat baked chicken breast(cooked at home) I put hot sauce on the chicken for flavor, then I add the chicken with a salad mixture, and then add six cruched up multigran tortilla into it, I would like to know if im am eating a healthy salad even though I add a few tortilla into it, also I exercise daily and drinks 148oz of water a day…..