Every joint in your body will be forced into the direction it can't go in naturally (e.g. knees bending into the wrong direction). In return, you can resize any object with your mind.

Literally every joint. All toes will bend into the wrong direction, your elbows, every joint in your fingers, your ankles will twist until you can't stand on your feet anymore. In some cases, the skin will probably rip (knees seem very likely).
Doctors manage to fully heal you after 8 months (though I'm not sure in what position you would rest in the hospital bed). The objects you can resize are literally everything, make your dog smarter by increasing his brain size, refill a bottle of cola by increasing the size of a single drop, shrink the car keys of your annoying boss to planck length, you name it.