Hi ! Good evening. I am Dr Shareef answering your query. As per the history of trauma, it could be a hematoma (collection of blood) in the axilla at the site of trauma. This should get absorbed of its own in due course. If it does not, or if it increases, I would get you assessed by a general surgeon, who might go for a mammgraphy of bilateral breasts followed by a FNAC (fine needle aspiraton cytology) and possibly a biopsy of the lesion. Further management would depend on the clinical examination and investigation reports. 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 health care magic to clear doubts on your health problems. Wishing you an early recovery. Dr Shareef.