Need help for ideas of a novel!

I love writing and my teachers have told me I have a talent for it and could definitely make a career out of it.
But, I can never think of good ideas for a book. It took me 3 weeks just too think up a topic for a short poem in english.
I want to make...

something like My sisters keeper, Twilight (minus the vamps..) something touching. something that just makes you cry. but I've never made anything like that. Any ideas?
Also, I always loose motivation quickly. never usually make it past the third chapter. How do I keep myself motivated? The knowing of it might become published just isnt enough..

P.S. I've posted this on other advice forums and only gotten rude comments that gave no advice. so I just want to add this,
I don't look up to twilight as literary inspiration, I like the style and feeling I get from it.
Like, its drama. and romance.
and once I have a small idea of a plot, I could make a whole book out of

how about someone's real story, like Marely and me
Write about someone on a ---
boat trip and a storm
falling in love and getting sick,
Loosing a loved one
suicide
loosing a child
getting a new puppy and how it changed your life
A dogs eye view to being in a shelter and getting a second chance with new home
Doctors and medicine
the ideas our endless, do what excitites you. Young girl having a dream on making the olimypic ( my spelling sucks) swim, hockey, team.
Good luck

Thanks! I like the ony about the dog in the shelter. it reminds me of my dog.
And a couple of them reminded me of my life. I could just tweak it to make it longer and more elaborate =] thanks much!!