I have an itchy anus. I have previously had hemeroids but have tried anusol and doesn't work.

Fiber, dry anus. Try taking a tablespoon of psyllium (such as metamucil) each day and apply calmoseptine around the anus 2-3 times per day for a couple weeks then as needed. If that doesn't take care of it, see a colorectal surgeon.
Yeast. Might be a yeast infection. Try a Nystatin ointment, cream, or powder. Don't wear a wet bathing suit for the several hours after swimming- dry off.