I think everyone has been given a gift (talent), be it art, writing, singing, playing music, etc. and its buried deep within us. It just comes naturally to us.
I also agree that we can have many interests or passions and those we have to find by focusing on a couple of interests and going from there. I have a passion for quilting, but I don't believe thats my gifting. My gifting is drawing but I've not nutured that gifting - its lain dormat for a number of years.
When I became interested in quilting, just as Sara did in gardening, I read books, took courses and worked hard at getting my quilting to where it is today. The same thing happened when I wanted to learn about gardening or making bears.
Don't give up on your song writing, but look at other areas you might find of interest to you. You'll probably find you have many different interests when you really begin to look.