4.5 weeks and rash, anyone else?

Help! This is my 6th pregnancy and I've never had this before. On Monday I started to get an itchy rash on the back sides of my upper arms. This then began to spread to my sides, under my breasts, and now it's on front my chest and has further worsened and spread. I went to doctor two days ago and he said its contact dermititis from my soap. I've been using that soap for several weeks though with no problem. So I've switched soaps to a hypoallergenic soap. The only other thing I've done different is I stopped drinking Pepsi and switched to an organic caffeine free soda, but I would think if this was from soap or soda switch that it would be everywhere on my body. My OB and regular doctor both said its not from pregnancy hormones but it started right at 4 weeks pregnant. Anybody else experience this? I'm miserable and creams aren't working to ease the itch.