Toxic Mage

You were born to poison.  probably sickly at birth, catching illness sickly.  Few people imagined much would come of you.  But power was dormant in you.  Some whisper of the power of green and copper dragons, but your power is more than that.  More likely you were born in a land subjected to some sort of blight, and that taint remains in you. 

Poison in Your Veins

Starting at 1st level, you have resistance to poison damage and have advantage against constitution throws for the poison condition.

You have a measure called a Poison Level.  it starts at 1.  Every time you encounter a new type of poison, after you take the damage and have cleared (if applicable) the poisoned condition, your poison level increases by 1.  you may add your poison level to your constitution throws against the poisoned condition

Poison in Your Skin

When ever you are struck by an unarmed attack or grappled, the attacker takes a number of d4 of poison damage equal to your poison level.  This has no effect on constructs or undead.

The damage increases at level 6 to a D6, at level 10 to a D8, and level 14 to a D10

Poison Attunement

You gain immunity to Poison damage and the Poisoned condition. 

Further you can secret your poison at will.  All of your weapons are considered poisoned.  During a short rest you can take an allies weapons to poison them as well.  In addition to their normal damage, they deal a number of d4 equal to your poison level.

Miasmic Cloud

At 6th level, as an action you may spend 2 sorcery points to create a cloud of poison gas around you.  any enemy comes within 20 ft of you or starts it turn in that radius must make a constitution saving throw against your spell save DC+ your poison level, or suffer a number of D6 equal to your poison level.

You may use this a number of times per day equal to your spell casting modifier

This radius increases to 40 ft at level 10, and 60 feet at level 14

Acrid Casting

At 14th level, you gain the ability to weave your poison into your spells.  If a spell cast with a spell-slot of level 1 or higher requires you to roll dice to determine damage, you may spend one sorcery point per spell slot level to change all the damage to poison damage. You may do this a number of times per short rest equal to your poison level

IF a spell would already deal poison damage, you may spend sorcery points to add extra die to damage roll up to your poison level.  You may do this once per long rest

Corrupted Biology

Starting at 18th level, You may use your Miasmic Cloud feature an unlimited number of times per day.

If you are hit with an attack that would deal poison damage to you you may instead regain the poison damage as HP, or 1/4 of it as Sorcery points your choice.

If you encounter a new poison or disease that would raise your poison level, it also restores half of your spent sorcery points.