On both breast, there is a patch of rashes which began beneath my areola/nipple and looks like eczema but seems to be spreading?

Ideas: A picture is worth a thousand words when it comes to skin problems. But a common skin problem on the breast, especially on the underside, is a yeast infection. You can try some anti-fungal OTC cream (ask your pharmacist) and see if that cures. If it doesn't then maybe consider making appt with your health care provider to appropriately diagnose.