Hello, I Am 4 1/2 Weeks Pregnant. I Noticed That

Hello, I am 4 1/2 weeks pregnant. I noticed that I started getting a rash on my legs & everyday it seems to be getting worse. My legs itch real bad & swell to the point I can not bend them & when I do itch them I get huge welts. At night it wakes me up & I lose sleep from all the itching. I went to my ob/gyn & they told me its dermatitis. I honestly can not take the itching anymore. it seems like I might be allergic to Benadryl spay that the Dr. told me to use. When I'm at work I can not obviously put ice on them. The question is, would a oatmeal bath be okay during pregnancy or what kind of things can help me get through this.