Answer:
I am the kind of nut that is empty at the center and has no shell.
I have fangs and enjoy piecing holes with a single bite.
I can swim but never get wet. I can run but never get tired. I follow you everywhere but never say a word. What am I?
I have no life but I can die. What am I?
When you stop and look you can always see me. If you try to touch you cannot feel me. I cannot move but as you near me I will move away from you.
No matter how little or how much you use me, you change me every month.