Apparently there are medications that you can buy over the counter. Ask your pharmacist for them, or in the article below gives the names of two medications are given, but those two medications appear to be by prescription only.
There is a simple test that you can do to check and see if you have pinworms. You will need some cellophane tape. See the article for complete directions:
Article from Mayo Clinic on Pinworm, for your information:
You will also need to be careful with clothing and bed clothes to prevent re-infection, and wash hands carefully. Wash the items in hot water to kill the organisms, if you have them.
I hope this helps.
If you have questions or comments, please reply so that I or another expert can address them.