Hey Mel!
I can think of a couple of suggestions you could try...
For the ideas problem, it might help to choose an idea, one you think you could develop the most, and try to plan it out on paper (or on Word). Make an outline, get down some info on your characters, stage the setting, and so on. That can be a good way of getting into the idea enough that you know what to write and feel like writing it and sticking with it. It can also be an indicator of whether or not the idea is going to work out, or how committed you're going to be to it. Sometimes you'll start to plan and realize an idea is too full of plot holes or doesn't make sense, or that it's too overwhelming to tackle for an easy project to get you back into the swing of things. Better to realize that at the beginning than start a new story, post a few chapters, and THEN decide you're in over your head.
As for original fiction, have you tried writing AU? That's the perfect bridge between fanfic and OF. You can still use the Backstreet Boys, but you're not as limited. Once you get used to writing AU, original fiction doesn't seem like a far stretch. I never used to be a fan of AU, but that's really all I'm writing right now, and I'm loving it. I still enjoy using the Boys as characters, so I don't see myself moving away from fanfic anytime soon, but it's nice to write about them just as people, not as pop stars, doing other things and living different lives. It lends itself to being more creative, I think, and it seems like it would be easy to transition from that to completely original characters in an original fic.
I hope some of that helps!
