I didn’t mean it that you must do it in polite manner. I didn’t express myself well. Tell him you are doing ok. “Thanks for asking” is more in line with “bless your heart” lol you can just say “I am ok”. Or say nothing

If you keep telling him you are doing ok, he’ll stop asking. He isn’t going to like it. He likes that you not ok so he keeps asking so it opens further communication about how you both not ok