You've been on many different diets. They seem to work for a period of time and then stop working. Have you ever wondered why? I am going to suggest that you don't need a diet, you need a lifestyle change.
Create A Plan
Eating right is a way of life. It isn't something you do for a period of time and then go back to the way things were. Taking control of your eating habits is a tough thing at first, but once you establish a plan of action and then execute it things get much easier. Examine your current eating habits and then make a plan that you are able to stick to. Creating an unrealistic plan will do nothing for you, it has to be something you can personally accomplish.
Make Small Changes
Once you have a plan and have identified how you will take control, break things down into very small steps. This, to me, is why eating 5 or 6 small meals a day works. I am able to be full all the time so I steer clear of snacks that might derail my progress. In addition, taking baby steps makes it more likely you will achieve those smaller goals and that gives you motivation going forward.
Change One Thing at a Time
Don't jump all the way in and change everything all at once. If meal preparation has been an issue for you, work on that until you've gotten it down. If eating 5 or 6 small meals a day is an issue, fix that before moving on. If meal timing has been an issue, work on that and get it under control. As you make these changes you will be building towards your ultimate goal of a lifestyle change that lasts.
Get an Accountability Partner
Involve a friend or loved one in your plan. Getting help from people who care about you will just make you work that much harder at being successful.
Celebrate Your Success
Make sure that any eating plan includes some reward meals. No, I am not talking an entire day of eating what you want, just a single meal during the week where you reward yourself for being consistent and sticking to the plan. Studies show that it is much easier to stick to a change like this if you have a reward meal to look forward to. Give it a shot and you will be surprised at how quickly you make the changes you needed to make.