You are right that affirmations don't work unless they're believable. And your T shouldn't be pushing you on them. I find most affirmations difficult to believe and opted to write my own which I could believe in, eg "I am working to heal and grow" instead of "I am worthy".

Here's something explaining why they don't work with low self-esteem, and what could be more helpful.

Why Positive Affirmations Don'''t Work