Too Lazy to Write Stories

I'm sometimes to lazy to write stories. Right now, I have to write four stories. I can be done with two of them if I added a few more chapters and ended it without making it really "interesting". But I don't want to disappoint my readers because they like this one story I have and I just made it really interesting so my readers are asking for more.

So my questions is how do you make yourself interested into a story again? And how do you stop yourself from starting to make a new story so you can finish an old one?