Hi,
What is your age? Have you noticed any abnormal features on breast self examination like skin changes, breast lump, nipple discharge , etc.
This could simply be skin lesions or some infective lesion.
You need to consult your breast specialist to get a proper clinical evaluation and to get relevant investigations if required.
You could apply calamine lotion and take some oral antihistamine medications for the itching. Wear lose clothes. This should help with your symptoms till you get to see your doctor.
Relax and let us know about what your doctor or breast specialist advises.
Let us know if you have any other doubts and post us about how you are doing.
Regards.
I'm not sure what the rash looks like.. but I was given some advice on one of my posts that said to look into inflammatory breast cancer... it starts with a rash from what I was able to research. Google it and see how it goes... Let me know what happens!!! Good luck.