Doesn’t work off charger.

My Apple Watch is not working correctly. I’ve had it on the charger for a while and the screen is on, says it’s at 100% charged, and I can do things on it. The minute I take it off the charger the screen turns off. When I play around pressing the two buttons it will light up with the Apple logo, but then that goes away and nothing happens. I’ve tried restarting it, tried the forced shut down, and tried updating it but nothing works. It can’t be the battery because every time I put it back on the charger the screen lights up and shows it’s fully charged. I’m not sure what to do at this point. It’s a Series 3, but I haven’t even had it two years at this point and it was treated like a fragile baby, never even going in water.