Can’t stick to a thought

I’ve been doing coaching and found it very beneficial. However I can only seem to stick to an intentional model/commit to a thought for 2 days. Then I return to my unintentional model without fail, no matter how many times I try to work through it. It’s building and really destroying my confidence in myself because of the piling evidence against me and I’m feeling hopeless in my goal to lose weight. Thank you for your time and advice.