I have rash around my anus appearing every month. it is very itchy and uncomfortable. what should i do?

Rash: as rashes are difficult to diagnose without seeing them, it would be best to go see your doctor next time you get this rash.

Pruritus ani? Yeast?: Everybody gets anal itching from time to time; the fancy medical name is pruritus ani (Latin for itchy anus). Or maybe a localized yeast infection. Show it to your doctor next time you get routine care. In the meantime, try an OTC yeast cream like Monistat® or any cream with active ingredient ending in "azole", plus maybe OTC hydrocortisone cream. But don't use HC alone; it could make yeast worse.