I rarely write one story at a time. Currently, I have two novels I'm actively working on, two other novels sitting on the back burners in my mind, and about a dozen short stories I'm in the process of editing, finishing, or sending out. This is my problem... this has always been my problem. Not writer's block, writer's blockage. Too many ideas trying to be born at the same time. It's messy, counter productive, and frustrating. I'm great at starting things. I suck at finishing them. This is why I really like short stories. I can sometimes get all the way through a short story while I get distracted when working through a novel. But, to be honest, this also happens with about half of my short stories too. That's why I have so many story starts.
Once I tried just focusing on one story and setting all other stories aside. I forced myself to complete the story. It was terrible, but finished. The next story I worked on I tried to do that again, but then an idea for another story kept demanding my attention so I gave in and worked on that too. It took more time, but it felt natural to work that way. So when thoughts about one of my novels kept saying, "hello! Pay attention to me!" I was attentive.
My main goal right now is to finish all the story starts I have. Will I start other stories in the interim? Possibly. But if I can just get one story finished, edited, and sent out each week (month?), I will be happy.