I had this last 2wks of my pg, and drove me totally insane! I tried a variety of things, and found the best to be Oilatum gel in the shower (nothing perfumed at all obv!), then when dry use either Lanacane powder all over, which is anti-itching, or Eurax cream which is anti-itch as well, and you can buy over the counter. All of these are safe during pg.
Keep as cool as possible, having cold showers and even putting damp teatowels on your bump or round your ankles (worst bit for me...still have marks 3wks later from where I broke the skin scratching) at night.
Hope this helps - you have my sympathies, I know how awful it is!!
Lucie & Iona 17 days xx