Did you add the extra socks inside your shoes or outside of your shoes? If inside, are you wearing the same size shoes that you do with your warm weather thin socks? If so, then you are probably causing part of the problem. You need some air in there to help keep your feet warm! 3 pairs of socks likely means you need a larger size shoe.

For winter riding, I use a slightly heavier wool sock (I use SmartWool socks, ultra-thin for summer, next level up but still not bulky) for winter), and I use shoe covers. If it's really cold, I also usually add chemical foot warmers. The ones I use are Heat Treat Toe Warmers, usually pick up a bunch at REI at the beginning of the season - http://www.rei.com/product/405012.

--- Denise