Blood infusion

You exchange a portion of life force for empowered spells. When casting, take 1d6 necrotic damage (this damage is unaffected by resistances or immunities). For the next minute when you deal damage to an enemy, the enemy takes an extra 1d6 damage of that type, If you use this spell more than once per short rest, roll a Constitution saving throw (egainst your Spell Save DC). On fallure, gain a point of exhaustion after taking the Initial damage.

The damage taken by both you and the enemy increases by 1d6 when you hit 5th level (2d6), 11th level (3d6) and 17th level (4d6).