The purpose of art is communication of truth in a manner that highlights particular aspects of it in revealing ways, that is, in ways that reveal something about it that might otherwise be lost or obscure. Self-expression might and usually will happen; every artist has his style, be he a painter, sculptor, composer or poet, and that style might very well help us to identify the artwork and understand it better, knowing its context. But the self-expression aspect of it is a by-product, a sometimes-happy bonus -- it is by no means the point of any good art.
To claim art primarily as a method for self-expression is to corrupt the praise-worthy humanistic and individualistic goal of the Romantic movement to its worst possible result; surely it is important to recognize the inherent dignity and worth of each individual, which is what many of the Romantics were stressing in their response to the soul-sucking Industrial Revolution. But, contrary to the belief of most of the modern world, it is not all about you. We are the crowing glory of creation, true enough, and that means that it's not all about you. It's all about us -- we.
Am I making any sense? I guess what I'm trying to say is, get over yourself. Look at the bigger picture. If you have something to say, or something to paint or write about yourself, place it in the context of the larger world; connect it to your fellow man, to creation at large. Move beyond yourself, and concern your work with more than your emo screamo self-indulgent melancholic brooding ruminations. Figure out your place in creation, and see what you can make of truth when you don't stop at you.