I had the same thing on my right forearm it was either the early months of my 2nd pregnancy or second trimester with my first. It itches horribly, I found relief with a paste of cornstarch. Took the sting and eased the itching down. It mostly bothered me at night so I would wrap my arm and leg it set over night.
It's an itchy, red rash that normally won't go away until after pregnancy.
Try cortisone cream. It'll help bring the redness down