I have the same problem. (it's actually quite common) I noticed it after having my daughter, and also a friend of mine has this issue as well, same scenario too. Your breast/nipple area develop the same sweat glands found under the arms and also in the groin region. So long as I don't get really hot or sweaty this isn't a problem. I just rubbed a deodorant directly onto the cups. A mildly scented or unscented aerosol deodorant may help also. I doubt it's a fungus honestly. If the odor is similar to underarm smell, then it's just sweat glands being sweat glands.