Jasmine wonders: I don't know how other writers do it. I have so many storylines running around in my head.
My response is ...
Jasmine, it sounds like you've opened Pandora's box of ideas, and, from my experience, there's no closing it, not without regret. You either write this story, and the next, and the next, ... or you don't, and let them die inside you. I've done both. I hate doing both. Writing is so hard and painful, but then readers (plural) tell me I've saved their lives with my writing? And I'm complaining about what, again? And when I let a story die, by not writing and sharing it? I die, a little and a lot, too. I wrote a one-chapter story that I was going to let die, because I was just too tired to write, and that story was deemed the best thing I ever wrote.
So, write when you are able, share when you're strong enough to, and even (especially) when you're not. You'll get attacked, savagely, when you truly open up and write from your heart ... I have. You'll make friends you'll've never have known nor made if you didn't write and share ... I have. And you'll look at that one piece you write, and marvel that you wrote that. Nobody else did. Nobody else could have. You did that, and only you. And you'll wonder if you can ever write that good again in your life, and the next time, even if it's four years later, you'll surprise yourself by topping that one perfect piece, without even trying (but crying and crying and crying as you write), and touching hearts that needed to read just what you, and only you, wrote.