Answer:
Weight in my belly, trees on my back, nails in my ribs, feet I do lack. What am I?
I'll bring out your bulls and slow your roll. I may even come out of your skull.
What is full of holes but still holds water?
What is that you will break even when you name it?
I am full of holes but still holds water.
No matter how little or how much you use me, you change me every month.