Let me start by welcoming you to 3FC, Mara.
And then on that note, there isn't anything wrong with you. I know exactly how you feel. I'm at my heaviest now of 280, and I have tried and tried to get in shape countless times, but I always lost interest about 2 or 3 days after starting.
What helps me is that I find stuff that inspires me, pictures of myself that I hate, pictures of the body I want, clothes I want to wear, inspiration quotes, and I put them every where I help motivate me. There is a tumblr called 1000 Reasons to Lose Weight that I found REALLY inspiring, so I saved countless pictures from it into a folder, and set them as my desktop. Changes every 10 seconds.
I think it's just important to keep yourself motivated.

"Don't give up! Even the word impossible say I'm possible!"