No following my plan

My question is two fold. I have figured out the thoughts but can’t seem to change them to something believable.
A. When I think about getting serious about getting back off sugar and flour, my thought is “what’s the point? It’s going to be hard and I wasn’t losing weight very well anyway” F: defeated A: inaction/eat flour/sugar R: no weight loss
B. Second circumstance: I’ve made a plan, written it down T: I can’t do this, I feel like crap F: incapable A: eat off my plan R: prove to myself I can’t follow a plan.
It seems to be a vicious stupid cycle. My specific question is: what thought do you all tell yourself to follow through. I have no believable thoughts in my arsenal – and I’ve tried quite a few on….