how to keep milk blister from reoccuring

3litttlebirds

I keep getting a milk blister in the same darn spot, or at least I guess it's a milk blister. It starts out as a clogged duct with nothing visible on the surface of the nipple. By the next day, though, if I'm unable to clear the clog, a white dot rises on the nipple. Once I scrape that off/pop that, the duct clears. How can I keep this from happening to I don't keep getting the clogged ducts.

I can't take Lecithin because baby has a possible soy allergy. Any other tips?