Chocolate DOES increase endorphin production, and endorphins ARE chemicals that make us happy, so there may certainly be some truth to your belief that it's more than a lack of willpower. I think it's debatable, but there is such a thing as chocolate addiction, and since sugar is also addictive, you may be caught in a cycle of addiction. I feel you though, chocolate is sexy, and I have questioned my own ability to let go of chocolate several times throughout my life. Some people are just prone to chocolate love, I think. Something that's helped me is buying (if I absolutely have to) good quality dark chocolate with the least amount of sugar possible. I have actually come to like it better, and while it may seem bitter or different at first, it grows on you quickly, and is much healthier for you. I also tend to eat less of it than the creamy stuff.
Exercise boost endorphins as well. Maybe you can try doing other things, physical things, when you start craving chocolate.
Also, how long has this been going on? Are you depressed at all or do you have a history of depression?
Maybe you're going to start your period.
Chocolate actually gives you "good feelings", it triggers certain chemicals in your brain. I also think that craving sugar can be caused by many things, like emotional eating. Are you relying on chocolate for energy, from what you have posted I think you have. I would suggest eating fruit and complex carbs that take a much slower time to digest and turn into fat. I eat hot oatmeal when I get those cravings and within 30 minutes my craving if I have them goes away.
Chocolate is a quick fix to up your energy levels, just like caffeine does. If you think you have an issue, I would suggest you speak with your doctor and rule out something physical. I used to crave it every single day, seriously. I got really sick end of Dec, and I have lost most of my sweet tooth, especially chocolate, I still have chocolate from xmas. It's too sweet, I may have a piece or two now. I was diagnosed Borderline diabetic this last month. I would suggest you get your blood sugars tested as well. I honestly wouldn't consider it an eating disorder unless you are bingeing on other things,.but to rule things out, check with your doc.