Chickweed! has been growing like crazy all over this fall, early winter due to the unseasonally warm weather. If you can do some weeding when the weather warms up, do so. Otherwise, you will have to wait until the weather warms up to use a bread leaf weed spray to kill it. Temperature usually needs to be in the 60's or above to spray for weeds. Good luck in eliminating this horrible weed from your yard.
(I, too, have a large patch of chickweed where we plant our spring lettuce. When it warms up this weekend, I hope to get out there and hand weed....ugh!)