May I know what is your age? Shingles will be manifested as a characteristic banded pattern of vesicular rash along with pain. Also it is highly unlikely that shingles will last so long without either aggravating or subsiding by itself. Do you have any lumpiness in your breast? I would suggest you to consult a surgeon to have your breast examined. Another thing that you should consider is to get an ECG done to exclude any cardiac pathology which might be manifesting as such a pain.