Medicine to treat pinworms can be purchased in Mexico at low cost with NO prescription. These are international quality brands. Mitafar, mebendazol, Ivermectin, albendazol. Fly into Mexico City and walk to any pharmacy. Stay at the Hostel Mundo Joven Catedral which is decent and cheap. Apply Noxema or Vaseline to your bottom to stop the itching. Place a cheap sandwich baggie on your hand to scoop up the Vaseline and apply. Use a new baggie each time. Wear disposal pants like Depends if you can.
You may need to take Albendazol 400 mg twice a day for several months. People have done this without serious side effects. Take it on an empty stomach.
A high fat meal makes the medicine enter your blood stream. You want it to sit in your intestines, not your blood. So don't take it with a fatty meal.