Bleargh! Accidentally deleted half a sentence in that last message. Should say "pick a favorite person or animal and draw 'em as a cave painting, classical sculpture, woodcut, religious-style icon, overdressed Renaissance royalty, pirate, Japanese print, Western gunslinger, Victorian fashion plate, art nouveau," etc.
Getting bored with your work usually means your creative self is impatient to try something different. I recommend playing around with styles and subjects you don't usually work with and see what happens.
Maybe set the fantasy aside for a while (however much we love seeing 'em here) and go do lots of quick live sketches and, I dunno, architectural doodles and silly cartoons and abstractions and caricatures or something. You can play with different eras of art, too; pick a favorite person or art nouveau, art deco, propaganda poster, comic book, and so on. If it's a person, you can try drawing them as an animal and a robot and a tree; if it's a pet, you could draw them as a person, and so on. Do an Arcimboldo-style portrait of someone 's face if they were made of fruit, newspapers, their favorite craft, or whatever else entertains you. Turn your muse loose in the toystore of the world.