I had about a week of crazy itchiness that drove me up the wall. I was especially itchy on my back and the back of my arms (ironically, my belly was probably the least itchy place). I usually get dry/itchy skin in the winter, so I think the pregnancy just exacerbated it about a million times. Humidifier running at night, then used cocoa butter, vaseline, lotion with oatmeal, and whatever super strength dry skin lotion I could find as often as I could. Also although it may seem counter intuitive, shower/bathe as LITTLE as possible, and avoid hot water. (Although I've heard of some people doing oatmeal baths, kinda like you do for chicken pox etc). Also, slather yourself with lotion like the second you get out of the shower when your pores are all open.
Another thing I tried that helped some was using ice packs where I was super itchy, which seemed to work some, although it might have just been because it was distracting.