Ok, I've had my harmonica for about a months now, and now I'm able to do some pretty cool bends. Only some of the notes, especially the ones you draw, are really hard to get a sound out of anymore. Is the harmonica worn out and no good? I though I remembered someone saying something about reeds getting dirty and needing to be cleaned. I've never seen the inside of a harmonica, so I don't know how reeds even work. How long to they usually last?