I'm wondering
No. It is impossible for a Pokemon to go down an evolution stage by all methods.
Source: Experience.
They cannot devolve once they are evolved as the actual trigger is when they level. Over here!
One way to PREVENT evolution is to press B while its evolving or give it the ever stone. You could also lay an egg of that Pokemon by breeding it with a Ditto. Before you judge your Pokemon first try to get along with your Pokemon. First let me know what Pokemon you're using. I know many ways to get along with any Pokemon depending on the kind.