Those are true Dutch white clover. A lot of plants look like clover but that is the real thing. PULL THEM IMMEDIATELY, because clover seeds like crazy. Do NOT let the clover form the white flowers. St Aug is usually a dominant force in the lawn against grassy plants, but it is a little baby against broadleafed plants. Even really poor plants will shade out St Aug. Your best defense is to mow the St Aug at the mower's highest setting - always.

Atrazine has a diminishing return when reused. I would not use it until at least mid spring. Wait for all the weeds to come back in full force and then blast them. And then don't use any more atrazine for a year. For now, it looks like your lawn is dormant. You might get away with spot-spraying some Weed-B-Gone Clover, Chickweed, and Oxalis. When St Aug is growing, the WBG will take it out, but when it's dormant, you might get away with it. To be more careful you could use cardboard as a shield so you only spray the clover.