I just wanted to let you know that pinworms are not always obvious--nor are they easy to detect. Personally I have had this anal itching symptom for a long time now, and have diagnosed myself with pinworms but had never once felt an actual worm until just last week, when I found one in the toilet.
If this is the issue, the itching will be very acute around 11 or 12 at night, so much that it can wake you up.
Candida is also characterized by anal itching--this is a yeast overgrowth that is irritated by consuming yeast or sugar.
If you have any other experience or knowledge of the infection, let me know!