I'm not a big believer in waiting for inspiration to write. I approach it as if I were an editorial writer for a publication, and have to submit a new story 3 days a week (for example). I sit down every day and try to write. Maybe that only lasts a half hour, maybe several hours...but I do it daily.
I've found that the more I write, the more I write. Sounds silly, but there's something about staying in that work zone that seems to feed creativity for me. I find it much more difficult, by comparison, to take a few weeks or a month off and then try to jump back into writing.
Not everyone has the luxury of being able to spend that amount of time writing, but almost everyone can carve out 15 minutes to an hour or so several days a week. This more disciplined approach has really helped me over the years, it might be worth a shot for you as well.

http://www.rogerbrownsongs.com
http://www.nashvillesongwriters.com/roger-brown