1. Read More. Feed your own imagination. Remind yourself of why you love stories and why you wanted to write any.
2. Remove the Pressure. Deliberately write just for your own pleasure. Make up complete nonsense. Have fun. (Later, if you can do anything with the writing, even if it is just the odd line or two makes it into a story, say, then fab. Even if not, you're taking time out to play with words and again remind yourself why you wanted to write).
3. Look at Where You've Come From Writing Wise. How much have you written over the years? Can you list publication credits (online and in print)? If not at that stage, have you had shortlistings? Are you simply submitting more stories for competitions than ever before? Remember you define what success in writing is. Yes, publication is the obvious goal but it isn't the only one. Saying you'll write 3 or 4 stories and then try and get them published later is a fine goal too. Look at what you've learned as you have written more. Have you learned how to improve your editing skills? Have you picked up tips on the way that are helping you write better now (I would be surprised if you hadn't)? All of these are good and worthy things.
4. Find supportive writing buddies via online groups or in creative writing classes. We all need to be reminded we're not alone. Others do understand our compulsion to write. Others understand the frustrations of trying to get published. You need that support. It can make all the difference during low times, creatively speaking.