This has been going on -- for four stinking months:
cnaThe infamous thumb brace
If you're curious, it's De Quervain's tendonitis. If you put your left hand in the position shown in the photo, and pull your thumb in tight against your hand, then you've just made a silly gesture with your hand because someone on a blog told you to do so.
If you then extend your thumb out to form an 'L' shape, and you want to scream with pain when you do so, you have De Quervain's tendonitis. Congratulations. Now quit doing things that hurt yourself.