I don't understand why after 4 hours aprox all the post that I do got "flagged automatically".

Every time that I post something, appears a red can over the post, and after 4 hours approx, the post dissapears from the sub-reddit. After that, I tell to a mod to fix the problem. Anyone knows why that happend? It's coz' my account is new? I'm banner? O don't really understand what to do, and I really want to post more, but idk..