Aww mama, that sounds really uncomfortable! A few of us moms in my circle have dealt with underarm issues while breastfeeding, and honestly it's best to check with your doctor or OB para ma-rule out kung ano exactly ang nangyari, sometimes it can be fungal, sometimes just sweat buildup from the stress ng breastfeeding, pero kailangan ng proper diagnosis. In the meantime, keep the area clean and dry, and try not to let your bra stay damp from milk leaks or sweat kasi that makes it worse. Kaya mo yan mama, malaki lang yan now pero fixable!