A cantrip that heals?! | Balancing and Improvements Assistance Wanted

I would say that a healing cantrip is only balanced if it takes an action to cast and does a d4 or less of healing. This is because healing is supposed to be a limited resource, so anything that heals 4 or more HP without using a spell slot starts to seem unbalanced. The healing could be upped based on the level of the player, like some damage cantrips (poison spray), but at least for tier 1, a d4 or less healing would be the most I would do. 

I have a Cantrip for a cleric of Shar

Share the pain 

A creature you touch regains a number of Hit Points equal to 1d6 and you take 1/3 as damage

At level 5 heal increases to 2d6 and you take 1/3

At level 11 heal is now 4d6 and the damage drops to 1/4

At level 17 heal is 6d6 and damage remains 1/4

 Cannot be used on yourself

(obviously can be adjusted to D4's)