That’s why quite a few MLB players swing the Axe batI am not a doctor and, like others here, my advice is to go to a doctor. Based on the location and description of how it happened, it sounds like it could be a hamate bone injury. This is fairly common, and it seems like a few players a year suffer this injury.
It could be something else entirely, but if it is the hamate bone, it's not going to just heal on its own.
There's some good info here, but again, go to the doctor for an actual diagnosis.
Stanton injury: Explaining hamate bone fractures
Miami Marlins outfielder Giancarlo Stanton suffered a hamate bone fracture. Here is the injury explained.www.fishstripes.com