I have pinworm and my stomach really hurts.. is this cause of the pinworms ?

Unlikely: Pinworms spend most of their time in the large intestine as passive hitch hikers. They cause no sensations at all unless they crawl out the anus &lay eggs in a sticky goo that triggers a skin reaction & itching.

Unlikely : Pinworms live in your large intestine and come out at night to lay eggs on your skin in the rectum area. It causes a lot of itching in that area. If you scratch you will get the eggs on you hands then when you touch something else the eggs stick on it and the next person who touches it gets the eggs on their hands . If these hands go in the mouth the eggs turn into pinworms in that person.