Wether you admit it or not, we all have our "I want to talk to the world" days and the "get out of my face - I want to be alone" days. We're human. It's natural. In fact, if you don't have at least one of those latter days, there just might be something wrong. I'm glad you're in a good mood 24/7 but it might not be healthy.
My point is, if your job is managing your business or organization's Social Media platforms, this can be an issue on those anti-social kinds-of days. Yet the job needs to be done. Your followers might be having a good day and expect to see engaging content, yet nothing is there because your creative brain is not functioning.
Again, we've all been there. It's nothing to get frustrated about. You just need to plan ahead for those days. It's called a Content Calendar. You need to set aside time each month when you can plan ahead and schedule what content you will post on which day, and what time, and on what platforms. You never know when a moment of inspiration will hit and you will want to want to record that moment of brilliance before you forget it. Not only write it down, but plan out when the best time will be to post it.
This will also help you to be more strategic with your overall Social Media Marketing plan. It will keep you on top of your execution strategy and reduce stress. Which, who knows, maybe will lessen those "don't talk to me" days, allowing you to be more productive.
Another way of boosting those creative juices is to not rely solely on your own material. Yes you are the social "expert" but there's a good chance that some of your coworkers around may have a good few ideas. They know the company as well and might have different perspectives on what kind of message should be portrayed on your platforms. Yes you still need to be the filter and decide if their idea coincides with your overall message and marketing goals, but it never hurts to ask around to gain more material for future postings.
Last, you want to remember that Social Media is completely separate from traditional marketing tactics. You are no longer yelling as loud as possible to get your targeted audience to listen and respond. Now you need to listen before speaking. See what engages your audience. See what kinds of conversations are happening and engage with them at appropriate times. By understanding your audience and knowing their needs, wants, and interests, you will better understand the particular message you want to portray.
Have fun with! The more stress you get about planning your strategy and content, the more rigid and unauthentic your message will be. It's social, so BE social!