I got a very itchy skin on my inguinal and perianal region, when i scratch it ,some skin shreds off and painful. what should i do doctors?

Get evaluated: Your doctor can help you. They will do what we can't thru the internet: first perform a visual inspection; digital exam after taking your history as to circumstances, duration, quality, timing of symptoms ; your risk factors. They may then determine topical treatment or ask to perform further evaluation. Problem may be dermatologic, infectious/fungal, inflammatory, functional, etc.

See an md: SOmeone should examine you, possibly a fungal infection or bacterial skin infection or eczema (allergy to something in contact with). Different treatments for each of these.