Answer:
Take off my skin I won't cry but you will. What am I?
You use a knife to slice my head and weep beside me when I am dead.
Long and thin red within with a nail at the end.
I am a vegetable that bugs stay away from
I'm not a bird, but I can fly through the sky. I'm not a river, but I'm full of water. What am I?
No matter how little or how much you use me, you change me every month.