Answer:
An action done on mosquito bites
While you were folding a letter you got me. Usually you will do whatever it takes to avoid me but now you can't help but find me.
When set loose I fly away. Never so cursed as when I go astray.
To cross the water, I'm the way. For water I'm above, I touch it not and truth to say, I neither swim nor move. What am I?
I have two bodies joined together as one. When standing still, I run and run. What am I?
No matter how little or how much you use me, you change me every month.