hi. it is best if you do a follow-up consult with your surgeon for physical examination and clinical evaluation. this thing sometimes happen after mastectomy with axillary dissection. it may be secondary to inflammatory reaction, which usually occurs a few days after the surgery and will spontaneously resolve. other concerns such as nerve involvement and lymhedema must also be ruled-out. diagnostics and management will be done accordingly. proper arm exercises/rehabilitation after mastectomy is also advised. hope this helps. good day!! ~dr.kaye