For some, sorcerers especially, magic is in their blood—for you, this is true in a more literal sense than usual.  Blood mages learn to channel the magical nature of their life essence, using it to empower their spells in ways never before seen with conventional magic.

Blood Magic

When your hit point maximum increases by gaining a sorcerer level (including at 1st level), you roll your hit die twice instead of once, increasing your hit point maximum by the total rolled plus your Constitution modifier.  You have a number of additional sorcerer hit dice equal to your proficiency bonus.  In addition, whenever you would spend 1 or more sorcery points, you can replace any number of those sorcery points with a roll of your hit die for each sorcery point replaced.  When you do so, the hit dice are expended and you take damage equal to the total of all dice rolled.  Also, when you cast a sorcerer spell, you can use Constitution as your spellcasting ability instead of Charisma.

Blood Mage Spells

Also starting at 1st level, you learn additional spells when you reach certain levels in this class, as shown below. Each of these spells counts as a sorcerer spell for you, but it doesn't count against the number of sorcerer spells you know.

Whenever you gain a sorcerer level, you can replace one spell you gained from this feature with another spell of the same level.  The new spell must be an abjuration or necromancy spell from the sorcerer, warlock, or wizard spell list.

 

Sorcerer Level             Spells

1st                                Cure Wounds, Inflict Wounds

3rd                                Lesser Restoration, Shadow Blade

5th                                Aura of Vitality, Vampiric Touch

7th                                Blight, Death Ward

9th                                Contagion, Greater Restoration

Retribution

At 6th level, you gain the ability to retaliate after being wounded—when you take damage from a creature within 30 feet of you, you can use your reaction to inflict 3d6 piercing damage to that creature.  The damage dealt increases to 4d6 at 11th level and 5d6 at 17th level. 

Siphon

Also at 6th level, when a creature is reduced to 0 hit points within 30 feet of you, you can use your reaction to regain hit points equal to your Constitution modifier plus your proficiency bonus.  If that creature was not killed outright, it has disadvantage on its first death saving throw.  You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Relentless Recovery

Starting at 14th level, your wounds heal more easily—when you regain hit points, you can gain the maximum number of hit points instead of rolling.  You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.  Also, you regain four expended hit dice when you finish a short rest.

Blood Savant

At 18th level, your spells are empowered when channeled through your blood—when you expend hit dice as part of casting a spell, the total rolled on those hit dice is added to the damage or healing done by that spell.  Also, you gain a +1 bonus to the attack roll or saving throw DC for the spell equal to the number of hit dice expended.