It sounds to me like you just placed the notes at random for this song. If you have trouble with melodies, you should try writing in a scale. I'd recommend starting with major, as it's the simplest to implement and understand (the white keys are tuned to the major scale!). Scales are simple to use because you're limited to certain notes. Don't think of it as "cheating" (probably around 90% of all blues music uses the same scale); it's just a tool for you to make music and have some fun!