What Is Required To Do OMAD

I am preparing for my upcoming hysterectomy, which will put me in surgical menopause and have been consulting with an endocrinologist and a dietitian and both advised me that I am likely to gain a minimum of 20 pounds unless I remove flour, sugar, dairy, grains, alcohol and do intermittent fasting.
More specifically, the recommendation was to implement a 20:4 or 23:1 (OMAD) protocol.

Today I am someone who eats whatever she wants whenever she wants and I’ve been trying to cut all the things they recommended and start the OMAD protocol but notice great resistance.
I did it for two days and then gave in to urges.

Each day I start the morning and am having the same recurring thoughts:

“One more day won’t change much.”
“I won’t stick to it.”
“It’s too hard.”
“These are too many hours to manage my urges.”
“I will feel deprived and hungry.”
“It’s very hard to start this protocol.”

When these thoughts come up they create for me over-desire, frustration, deprivation, and self-doubt, and I then give in and immediately overeat.
I tried to swap them with new thoughts like:

“Yes, it will be hard at first but it will do me good in the long-run.”
“I want to be a woman who can endure hunger and deprivation.”
“I’m not going to die from temporary hunger.”

But it’s almost as if these thoughts don’t “work” and my brain stays completely unfazed by them.
They are weaker in comparison to the default thoughts.
Am I then doomed that unless I find a strong thought I won’t be able to endure the fast?