I also write alot, which probably helps.
Maybe thats why i'm so obsessed with making songs with stories, and why ultimately I decided to side with classical.
OH, on another note (I lol at my play on words) another great way to come up with melodies, is listening to the type of music you want to end up making.
People who draw in a certain style are told to follow three steps
1) find pictures and drawings to the style you want.
2) Trace those pictures, and get your hand used to drawing in that style.
3) master the style, and then make it your own.
I like to think audio creation follows similar process, except don't TRACE the song, cuz thats gonna get you destroyed by your peers and etc, but try to understand what they use, and how they use it, and where, and eventually you'll break it down into steps small enough to manipulate it into your own liking.
Also, for the first couple of months, the songs in your head you hear, you will more then likely not be able to create them. Think of it like this, imagine a great drawing, and then get some paper and draw it. You're not going to be able to, because you know how it SHOULD look, but you lack the skills in getting there. Audio creation, EXACTLY the same thing. Just keep busting them out, i've hit my 250 song mark, and i'm still struggling to get it down perfect.