i'm sorry to hear you're dealing with this. a number of different conditions could cause the type of sore you're describing. your best bet is to have it checked out by a health care professional. it could be something simple like a boil but an open sore any place on the body should be evaluated due to the possibility of infection. meanwhile assuming you have no medication allergies you're probably safe to clean the wound gently with plain soap and water and then apply some over-the-counter antibiotic ointment (like generic "triple antibiotic ointment"). that's just a short-term fix however this will not cure the problem. wishing you all the best!
i have a circular sore with an open hole in middle of it located on a cheek of my buttlock. it has slight purple hue around it and hurts when touched.