Hello. Thanks for asking from HCM. I can understand your concern. This cyst needs evaluation. I am giving you list of most common scalp lesions with there features. You can correlate your features and reach unto some conclusion : Sebaceous/dermoid cyst - It is firm, scalp swelling, mobile, well defined margins and usually painless. Pain can occur in case of infection or reaction. Swelling becomes red, warm, tender and sometimes rupture and leads to pus discharge. For treatment of infected swelling, swelling needs excision along with antibiotic therapy like co-amoxyclav. For this, you have to consult doctor. He/she will send it for biopsy and confirm diagnosis. Usually no further treatment is needed. : Bony swelling like osteoma/fibrous dysplasia : It is firm to hard, immobile, skin mobile over it, margins continue with skull bone, may be painful. For treatment, you need to consult doctor as surgical excision is treatment. For small swelling of 1 cm or less, it can be observed. Pain can be treated by taking painkiller Diclofenac sodium after proper prescription. And regarding breastfeeding, you are right that every drug which you will take, it will be secreted in milk. You can take antibiotic after consulting it with doctor. Hope it will help you. Take care. Thanks.