The ability to move up and down the neck of a guitar and understand what your available notes are in any given fret, is something that many guitarists struggle with well into their careers. It takes an effort to commit oneself to learning where all of the notes are and the patterns they create, but that doesn’t mean it has to be difficult to pick up this skill.
If you already have some lyrics written, really think about how a motif would work with your most important words or phrase. Start by saying them out loud in a few different ways. This will give you a really basic idea of the rhythm you might use and an inclination of where the pitch naturally rises and falls. Use your phone to record yourself.