Hi, I can understand your concern for the bump near butt cheek. It will be practically impossible to give exact cause of the bump without a facility to examine it or without a picture. Even then amongst the most common of the possibility be a simply over proliferation of oil gland and hair root known as folliculitis or simple pyoderma. Do not pinch, pop or squeeze or even not touch the area unnecessarily as it can cause infection at this area. You can take antibiotic such as cefadroxyl 500 mg twice or ciprofloxacin 500mg twice for 5 days. You can apply fucidin or mupirocin cream very lightly over the affected area. Take care.