It's hard to say considering I've never seen you pitch. But, being 13 years old I take it or somewhere near that? you might be worn down. When I was that age, there was only one league in my area and we only played 12 games a year, so I don't know.
But if it is a mental thing, it can't hurt to try the visualizing. Either way, if your worn down, the curve would probably make that even worse.