I have heard of a condition before called PUPPS but don't really know much about it. Found this on www.allthingspregnant.com -
"A common rash during pregnancy is Pruritic Urticarial Papules and Plaques of Pregnancy. This is a most unpleasant rash with an incredible itch that's only cure is delivery of the placenta. Although this is most common in first pregnancies, it has been known to occur in subsequent pregnancies. This problem affects one in about 160 to 200 pregnancies.
The onset of this rash is usually the third trimester but it has been known to appear in the early post partum period. The rash starts on the abdomen and then spreads to the extremities. It is an unbearably itchy rash. Happily the rash doesn't normally spread to the face. After delivery of the baby, the rash and the itch rapidly disappear.
Treatment of the rash is at best a mask. Benadryl is a safe and semi effective way of controlling the itch as well as a few prescribed topical ointments. As well, cold compresses, oatmeal baths help. Prednisone is not always prescribed unless the itching is unbearable.
This is not a pleasant situation to have to face during pregnancy, but there are no known ill effects on the baby. Some doctors believe this to be an allergic reaction to the placenta but they also have noted a relationship to maternal weight gain, newborn birth weight and the incidence of twins."
To be safe - Call your doc!!
Take care and congratulations :)