If the battery in the Watch became very hot during charging there is something seriously wrong with the battery. If you live close enough to visit an Apple store you should get a diagnostic done at the Genius Bar. Your battery likely needs replacement. If so, they’ll quote a price for the battery replacement.
BTW, just before the battery problems started how long was your battery lasting before needing a recharging? Also, was there a thermometer icon on the screen when you took it off the charger? This means that the temperature of your Apple Watch has exceeded safe operating temperatures.