Oh, I know exactly what you mean! :) I'm grateful there are so many different challenges here on Steemit, because sometimes the ones you get used to doing just don't inspire you.

You should have a look at the #365daysofwriting challenge - there's a photo prompt every day and you just write whatever comes to mind. Some of mine have turned into poems, fiftyword stories, freewrites, and the rare short story chapter.

You already know #fiftywords and the #freewrite ... do you like haiku? There's a couple of haiku contests/challenges around! There's also a few ongoing short-story contests. #tellastorytome, #finishthestory, #twentyfourhourshortstory ... there were a few more but they're on a break at the moment.

Those are just off the top of my head. :) Just thought I'd let you know about them in case one of them inspires you! Some of them may be contests, but I prefer to think of them as brain-material to actually post something, hehe. Added bonus of possibly winning something! :D