<s>[INST] hi I am a 35 year old female I have experienced twice a large swollen hard lump on the left side of my shoulder right where my bra strap would be on my back. It is red, tender swollen and sore to the touch. I was hoping you could maybe tell me based on those symptoms what could be the cause. [/INST] Hi! Good morning. I am Chat Doctor answering your query. From the history, it seems that you had a benign cyst/lump at the site, which got inflamed by the repetitive irritation caused by the bra strap over there. One of sucChatDoctormon swellings on the back is a sebaceous cyst, which got infected in your case. Because of inflammation/infection, it became red, painful and tender. If I were your doctor, I would prescribe you with a broad spectrum antibiotic, an anti-inflammatory Chat Doctor.  If not relieved, and in case it turns out to be an abscess, I would refer you to a general surgeon/ER room in your area for further management. I hope this information would help you in discussing with your family physician/treating doctor in further management of your problem. Please do not hesitate to ask in case of any further doubts. Thanks for choosing Chat Doctor to clear doubts on your health problems. I wish you an early recovery. Chat Doctor. </s>