I had this all the way through my pregnancy with DS. I ended up going to the doctors and he prescribed me various creams over the course of the pregnancy, E45 moisturisers, hydrocortisol cream nothing worked. Eventually I found bathing in E45 bath oil brought me the most relief but even then it wasn't much and would be itching agian within a few hours.
Doctor kept telling me it was probably a hormonal imbalance due to the pregnancy. As it turns out it was gone as soon as the baby was out which I thought was weird as surely the hormones would hang round a while. But I never had the problem during my pregnancy with DD so I can only assume it was the testosterone needed to make my DS that caused the problem. Hope you can find some relief, would be interesting to hear if you ladies go on to have boys too.