I know how you feel. I really do. I have fallen off the wagon so many times it's not even funny.
I wish I had a magic pill that would work. The best advise I can give you is to make a plan and stick to it. Yeah, not that great lol.
There must be something in your plan that makes it hard to stick to, do you have any idea what that is? Are you over-complicating things? Perhaps if you write down what you want your plan to be, but don't include more than, say, 5 points or so?
I don't know about you, but personally I get overwhelmed when I try to change in one bazillion ways at the same time, whereas "I count calories - anything else is a bonus" is a bit easier to constantly keep at the front of your mind.
Best of luck to you! It CAN be done!