The cause of your diet related problems: Sugar
Is sugar a trigger for you? Are you a food addict? Have you got the exercise down, but have yet to commit to a healthy diet? You've heard it many places, moderation is the key. But this is not always the case. Odds are, if you are unhappy with your eating habits and health, there is a problem. You probably eat your emotions, eat when you're bored, stressed, just because a food is yummy and you want more and more, because you're out with friends and they're eating, because you like to bake, because you crave it, it's that time of the month, your bf left you, the reasons are nearly endless.
If you've gotten in the habit of eating an unbalanced diet, the best thing you can do is to remove the problem. Sugar is in everything these days. Peanut butter, bread, crackers, frozen dinners, canned fruit, cereal. There are tons of healthy foods you can eat, but until you cut out everything with that little white drug in it, it'll still have a hold on you and will hold you back from fully reaching your goals. It'd be like telling an alcoholic to have alcohol in moderation, they may be able to do it (just as some people MAY be able to only eat one cookie as a snack) but your brain and body are accustomed to whatever amount you currently eat, and once you start, that chemical reaction is going to start and you'll likely be tricked into going until you reach your limit.
So, to sum it up . . read food labels. Odds are, if it's got more than 3 or 4 ingredients, it's not good for you. And then . . remove all sugar from your diet. Get yourself out of that cycle! You can do it! Say it, believe it, remove it all from your house, and do it!