Make sure it's not cholestasis.
I'm having the same problem right now. In fact, I just got a rash today from all the Shea Butter I was applying haha. The doctor told me today your skin is extra sensitive during pregnancy so stress, fabrics, hormone changes, perfumes etc can cause irritation or a skin crawling feeling. They gave me benadryl and basically said it would pass. I'm 29 wks.
I had this itch with my first child to, but mine also felt as if it was inside my body...almost like an allergy. It was driving me crazy, alobg with acne...that was also itchy! I ended up at the doc cos it was so bad...he gave me a gel for the acne, a suppository and a capsule for vaginal use...yes...the itch was there too. It worked like a bomb. My docs explanation was that it could have been the clash in hormones...mine and the little boy I was carrying. I would have it checked out if I was you..it was really uncomfortable for me!