You write that the Chofetz Chaim writes that one should not say lashon harah about ones self. Where in chofetz chaim does it say that? I couldn’t find it.
The source for not saying Lashon Hara about oneself is from a famous story. The story is presented in several books, such as "Meir Eyney YIsrael" - Stories about the Chofetz Chaim. Indeed, in his book, the Chofetz Chaim dosn't bring this prohibition. Perhaps the reason is that this prohibition is not because of laws of Lashon Hara but other reasons such as Chilul Hashem (desecration of God). The Rambam in the laws of Tshuva (B, E) specifies cases in which a person must not publish his sins publicly. Rabbi Yisrael Wende