Since this has lasted for a couple of weeks and sounds uncomfortable, you will definitely want to show the doctor.  Don't use the Cortizone cream anymore unless the doctor gives the OK.  For some problems, it could be exactly the wrong thing.  I'm also not sure whether it's OK in pregnancy.  Check out this column for more information about rashes.  One type of breast cancer called Paget's Disease of the breast presents with an eczema-type rash around the nipple.  But I think there will be a benign explanation for your rash.  Pregnancy causes so many skin changes.  You'll probably be seeing the doctor soon, but why not call tomorrow and describe the rash?  The doctor might have some suggestions before your next appointment that will relieve that itch.