Amulet of The Elements

This amulet crafted from bone has small runes carved into it that represent the elements.
The wearer of this amulet can use this a cleric holy symbol, furthermore this amulet has four magical charges that reset the next dawn.
After the wearer casts a cleric spell that inflicts damage on a target they expend a magical charge and have one of the following happen to a target:
Fire: The target takes 1d6 fire damage and at the start of their next turn must make a constitution saving throw or take an extra d6 fire damage.
Water: The target takes 1d6 bludgeoning damage and must succeed on a strength saving throw or be knocked prone.
Lightning: The target takes 1d6 lightning damage and must succeed on a constitution saving throw or have disadvantage on their next attack roll.