One might find it useful to distinguish between someone who writes both words and music (songwriter), someone who writes words only (lyricist), and someone who writes music only (tunesmith?). Now, "lyricist" is probably pretty clear to everybody, "tunesmith" should be fairly clear but I can't help but think there's some better/classier word for it, and "songwriter" could probably mean any of the three, depending upon the context and/or one's personal idea of what the word signifies. If you feel it necessary or helpful to indicate that you normally write the music only, you might consider "tunesmith" or some equivalent. It seems that everyone here has a pretty high opinion of what you do, Mbo, and it's just a matter of how precise you want your terminology to be.