Yes I got your problem. Bingo.
Hi and welcome to HCM. Thank you for posting your query.
1st thing is your doctor did a wonderful job by looking for all the causes that you mentioned. He's spot on.
More than 90 percent of the times, all the three causes you mentioned in your question leads to such itching problems.
Most importantly, I need your gender and age.
The symptoms that you tell are classical of some kind of infection namely
Enterobius Vermicularis.
That organism will come out in night and go back into the
rectum, vagina day times. But it generally happens with women, not with males.
So I strongly suspect this infection.
You can do one thing,
1. Take Tablet
Albendazole 400mg night time. 1 dose
It should be enough for 6 months.
If symptoms persists, then you you can take 3 doses, spanning one week difference.
This should solve your problem. In case you need any further help, feel free to contact me.
Take care.