Answer:
No matter how little or how much you use me, you change me every month.
When set loose I fly away. Never so cursed as when I go astray.
Find an English word that uses all of the following letters: PNLLEEEESSSSS
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.
What two things can always see what the other sees, but can never see each other?
You use it between your head and your toes, the more it works the thinner it grows.