At the start of my preg i got a really itchy back and boobs. I also got really dry skin just on my chin, looked like a rash. Went to the doc and had it checked and she said its just the pregnancy taking moisture from my skin. Try using something like Dove body lotion (or something else, i found it needed to be really oily) twice a day, thats what stopped it for me. But if i forget even once i gets really itchy again.

I've tried Cocoa Butter and that didnt work but 'Bio Oil' did so like i said maybe something oily. Best to check with your doc too though just in case.