What should I look for in medicines for a skin allergy if I'm pregnant?

Skin Rash. Start with topical anti-itch creams (1% Hydrocortisone and/or benadryl). If you need to use an oral antihistamine, both zyrtec and Claritin (loratadine) are safe in pregnancy. Allegra is not safe in pregnancy. You can always ask your OB or an allergist.
Hydrocortisone. Hydrocortisone can be used along with barrier repair creams. If not effective stronger creams are available with permission of your ob.