I know what you're thinking. But the answer is no, you're not less of a writer than Stephen King or any other writer just because you're tired of writing. Writing short stories is often challenging and grueling work. That's the key word, work. Writing letters, journal entries and love notes are also forms of writing but do not require a great deal of work.
Short stories are all the more challenging due to their restrictions on word count and space.
Short stories are required to deliver what novels deliver but in a lot less space and with a lot less words. If you've reached a point in your story or draft that you just can't think or proceed any further. Go see a movie, or enjoy a nice dinner. Once you return from your adventures, if you feel up to it, take a look at your story again. Perhaps while out, you had some ideas that might work, or discovered a new plot twist.