No. It is impossible for a Pokemon to go down an evolution stage by all methods.
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.