Just a thought. Have you tried a course of DEC - Diethylcarbamazine.
I have no research on its use with pinworms, but it is commonly used for filaria, Loa Loa and River Blindess worms by the World Health Organisation.
These worms all live in the fatty layer under the dermis. IMHO despite opinion to the contrary I believe that skin mites live there as well. This is the reason I began the trial.
By Day Two after beginning it activated old scars into raised itchy ted nodules which then disappeared completely. One of them now has a dent under the skin.
DEC is said to alert the immune system to the presence of foreign bodies and is also said to destroy the eggs of Cutaneous (skin) worms. My hope was that it would target and allow the immune system to destroy mites eggs. I believe strongly it is doing exactly that.
It is possible the pinworms are being killed but their eggs are not and the infestation is reactivating. It is also possible the DEC will kill pinworm eggs.
The only side effect I have had is some nausea on the first and second day which was quelled with 5mls of original Benadryl.
This medication is available in Australia from The Vet Shed in Brisbane and the company will ship overseas. I do not know if customs would have an issue with it coming into the US or other countries.
I personally use the WHO dosage for River Blindness worms and filaria which is 6mg/kg body weight divided into two doses per day.....for 21 days.
I will post again after the course is finished.
I have undergone two lengthy courses of Albendazole and while this seemed to kill all live mites, after seeing the reactions of my skin after taking DEC I believe there were hidden nests of eggs.
The Albendazole also did not address the live mites in deep nests on my feet, I believe due to the deep nodules formed by the mites which do not allow penetration of with oral or topical parasitics.