Cheating?

I love writing ... I always have and I think I always will. It's my one escape, the thing that keeps me sane when I'm in a house full of people that have the ability to drive me up the wall. I've always been told that I am a good author as well, the only problem is I can only get ideas that have already been done. 
Now I'm not saying I copy my ideas from well known books but I have a very specific style and that's fantasy. I've tried to get away from that by writing something real, something that relates to me but somehow I can't get my head around reality, it all seems too mundane. My style is magic so I write about it. However it's a genre that everyone is into at the moment, which is a problem for me. I just seem like I'm copying other authors ideas, just because my mind works on the same wavelength. I've written a book, more of a story that goes on, but the problem is it's so much like Twilight. I don't understand. Why does everything have to be so similar with vampires and werewolves? It's frustrating !! 
So right now, I've given up on my own creations and I've turned to my old teenage ways of writing Fan Fiction. Now, this I cannot decide on. 
Fan Fiction is something fans write, taking a very well known book and twisting it, mixing things up, bringing in new characters and creating new character relationships. Now I enjoy doing this, I have many Fan Fiction folders, and my favourite has to be my Harry Potter fanfic. I'm a huge fan of Harry Potter and a lot of my stories are based on the books, just messed around a bit. But I can't decide whether it's cheating or not. Is it just a practice exercise for authors to explore their own writing style, or is it really cheating to take another authors ideas and make them their own in a blatantly obvious way? I would have thought I would feel bad if I wrote fanfic but I love it too much. There are so many ideas rolling around in my head, relating to Harry Potter, and it's almost frustrating that I can't think of anything else this good with my own plots!! 
Will I ever be a well known author? Will I ever get my dream job or am I ruining it as I type each Harry Potter related word on my laptop? I suppose I'll find out sooner or later but in the mean time, I'm having too much fun writing to stop !! 
So I just want to let you all know, if it makes you happy, keep writing it! Forget what people think and do it your own way :)