|wow, that sounds incredibly uncomfortable and disgusting and bad and horrible and all those good negative feelings.
I can understand why oral steroids would be bad while pregnant. Would you be able to use a topical steroid? I don't know if they're as effective, but it may help a bit.
Have you tried seeing a dermatologist, rather than just a doctor? Maybe they know something the doctor doesn't.
I don't really have any suggestions except all those temporary things like oatmeal baths and baking soda baths. Maybe getting a second opinion from another doctor can get you towards a better direction.
Anyway it goes, good luck! I hope that goes away soon. It sounds like a really horrible position to be in.