It isn't just Walmart. Our eggs at both Ralph's and Aldi's went from $0.77-0.88 to $2.69/dozen in two weeks. I picked up two dozen for $3.69 at Costco today, though. Still not as good as your price, but better than anything around here.
NPR suggests that it is national, and that it is just due to people like us gorging on eggs while they were cheap.