I have been reading through the rules a a pretty fast pace these past few days. I remember something about being able to buy extra wounds for xp, but I can't recall where in the book that was or what the cost was. All I remember is that it was 1d5 extra wounds. Any help would be good, thanks.

You read incorrectly. You can buy ranks of the Sound Constitution Talent, which adds one wound per purchased rank. You may have been thinking of using Fate Points to recover 1d5 noncritical wounds.

Looks like Errant is right here.

The Sound constitution talwen gives you 1 extra wound each time you buy the talent.

With FP you can regain lost wounds and that = 1d5 (though most GM's allow the players to regain 5 wounds that way)