I'm the same way about stories. I've tried to do short stories, but they always end up so much longer! It can get frustrating, but plugging away until you have a completed story is rewarding in the end.

I've had a hard time trying to differentiate between characters sometimes too. It helped when I stopped trying to make character outlines in the beginning. It isn't for everyone, but sometimes going by the seat of your pants can help give spontaneity to the story and the characters.