What can i use for this itchy red rash underneath both of my breasts? i'm really big breasted and they sweat and cause this irritation.

Antifungal cream: It is common for women to get a yeast infection under their breasts especially in the warm weather. The best treatment is to use an over the counter yeast cream like lamisil (terbinafine) twice a day unitl it is resolved. After it has resolved start the treatment again at the first sign of new infection. When applying the cream use a thin layer only.