Suggest Remedy For Pain In Buttocks

Hello I have sore buttocks dont know why like the skin and cheeks hurt. My age is 58yrs female 5'4ins tall 163cm 143pd 65kg. I have had a history of Melanoma but nothing active for 6yrs. I have aching buttocks even when I get up if I sit for a short time I walk and do water exercises and always moving. I dont know why this has only started in the last month or so? Thank you for your time.