You may have PUPPP. You can read about it and see a pictures here:
http://en.wikipedia.org/wiki/PUPPP
and
http://dermnetnz.org/reactions/puppp.html
I had this when I was pregnant with my first DD. I was absolutely miserable. At that time (11 years ago), my doctor would only allow me to take baking soda baths. I hated taking baths and would be absolutely miserable all day and night so I would take a container of water and baking soda and use a wash cloth and apply it to my skin. There were times when I would wake up in the morning just covered in white from the baking soda.
I would check with your doctor to see if it is safe to take Benedryl (I believe I read on another board that a mother-to-be was able to take Benedryl to help relieve the itching).
If you do have PUPPP, I really sympathize with you. Delivering the baby is the only thing that will get rid of it. I remember being in labor and having my ankles itch really bad. I had an epidural and had no sensation in my legs so all the scratching did absolutely nothing for me because I couldn't even feel the scratching.
(ETA: Looks like Deb T and I were posting at the same time with the same answer.)