I completely relate. I can’t think of any trauma but i used to have episodes of really bad thoughts. Barely anymore. I wouldn’t know how to teach you to stop that because it wasn’t one single thing, it was a whole journey that i’m still on. It’s might also not apply to you very well. But I can give you some things to consider:

• trauma is not just something terrible that happened to you. It could just be a small negative interaction that as an adult you wouldn’t think twice about, but as an impressionable, clueless kid it really stays with you
• it can also be what didn’t happen. Maybe you didn’t get the time and attention you needed. Or you got praised for being “mature and uncomplicated” which actually meant “thanks for hiding you needs and problems so i don’t have to deal with it” so you never had anyone to rely on
• Bad thoughts tend to completely take over because they always seem important or interesting. If you do some introspection you might find they are just silly. Once you understand and truly believe that, you can just decide not to have them
• For me that last point was heavily tied to my self esteem. For that it helped me a lot to contrast some thoughts but looking through a mirror and see how an interaction would be with the roles reversed. e.g. you thought you were rude to someone but with the roles reversed you wouldn’t think anything of the same interaction

i’d be more than happy to discuss this at length if you’re interested