Despite everyone's beliefs that you wouldn't make it through childhood, despite the health scares and sickness, broken bones and fevers, you persist.  Though you may not be the pillar of fortitude, you have an inner fire that cannot be extinguished.  You gain the following benefits:

• Your Constitution score is set to 9.  This can never go higher though it can go lower.
• If you should fail a Constitution saving throw, you may reroll it.  If you choose to reroll in this way, you gain 1 point of exhaustion.  You may only do this once per long rest.
• When you level while you have this feat you may roll an additional d4 when calculating hit points.