Do you think hives could be related to your pregnancies? Is this is your third one?
I never had allergies until my first pregnancy and they stayed with me for quite a while after that. No science talk here but lots of gal pals complained of allergy onset with their pregnancies. Hormonal fluctuations and all.
Here's a MedHelp link about pregnancy and hives (urticaria), if you want to read other pregnant women's experience with this problem, and what meds they discuss as safe. And there's a doctor on that thread:
http://www.medhelp.org/posts/Allergy/Urticaria-hives--pregnancy/show/441583
I would natch check ANY med you take with your obstetrician.
At some point after the baby is born, get yourself referred to a good hepatologist and schedule a liver biopsy (which is no big deal) to check on your liver health.
Best wishes for an easy delivery and a healthy baby,
Susan