You could have mastitis or a similar infection again, so if you run a fever, call the doctor right away.  Some kind of trauma you don't remember might be causing the pain; if so, it will soon go away.  If it doesn't go away in a week or two, or if it gets red and swollen, make an appointment to see the doctor.  There is a possibility that this could be an early symptom of a relatively rare type of breast cancer called inflammatory breast cancer.  I hesitate to mention this as a possibility because it is much too soon to panic about a rare cancer.  However, every woman needs to know that not all cancer starts with a lump and to check with a doctor for pain and tenderness that don't go away in a menstrual cycle.  I hope the pain soon goes away as quickly as it came as so many breast pains do.