On the day the right-clicking stopped working, do you recall changing any settings, downloading any mods, or pressing a strange button on your keyboard? If so, that might be the case.
If you can't remember, try experimenting with your mouse. Can you see the cursor on the game? Does your character run to an arrow where you clicked with the left side of your mouse? Have you tried just pointlessly spamming the right and left sides of your mouse until everything worked again in the game?
These aren't great suggestions, but if nothing happens I'd recommend just using the arrow keys like Shurtle said above. I do hope at least one of these things work