Hi and sorry about your pain and boil. Does it have pus? Do you have a fever? If it isn't going away you should have a doctor take a look at it. I don't know if it is causing your pain. It could be deep and pinching a nerve but I can't say. Also have you tried topical antibiotics on it? You may need oral antibiotics if it is an infection. Try warm compresses on it and see it it gets better. But I still think you need to get into see someone.
How are you? Do you still have the pain and skin lesion in your back? Indeed back pain could be due to musculoskeletal as well as neurological issues that warrants further evaluation. Skin abscesses usually respond well with antibiotics and symptomatic management. If it persists, it is best that you have this checked by your doctor for proper evaluation, Direct clinical examination is important. Take care and do keep us posted.