The gym is the easy part. It's the diet that separates the men from the boys. Like Aaron said, use the candy bar or w/e as a "cheat meal" NOT cheat day. Keep it in moderation and TRY to have something of nutritional value. Here's my last cheat meal dessert
Sweet potato banana protein pancakes with protein sludge. Nutritious AND good.
OP stick to it I'm going on 3 months of eating much better and while it is hard at times as long as you don't pig out on bad stuff you can have a candy bar/cheat MEAL, a snickers bar is mine, or a grilled burger say once a week if you've earned it. I'm down about 20 pounds with no intention of looking back. P90X is pretty legit I've done a few days worth of training with it mainly when I didn't have access to my gym. Just stick with it and it'll get easier to work out and eat right.