We'll pray with you, mama.
Would you consider an idea that is totally out of left field? If so, read on... One thing that reduces incidence of mastitis in cows is the use of something called teat dip. It's basically an antiseptic wash that is applied right after milking, reducing the infiltration of mastitis-causing bacteria into the teat canal. Ordinarily I wouldn't even mention this to a nursing mom, because I'm a big believer in people not trying to kill off the normal bacterial flora on their skin. Antibacterial hand soap? No thank you! But what if you happen to harbor some strain of bacteria that gets into your nipple pores, and then causes these plugs to form, perhaps as a response to the bacteria? I'm thinking that an experimental approach you could take would be to wipe down your nipples and areolas with some sort of germicidal solution. I'm thinking rubbing alcohol or antibacterial soap or an antibacterial gel. Of course, you'd wash your nipples and areolas again before nursing baby.
Sorry if that's too crazy for you!