Hi Molly
I didn't have hives during pregnancy but have had my shares Prior and Post.. For me, that which brought it on was STRESS .
From all that I have read about hives on the net, it seems once you have hives, they run a cycle. the cycle can vary in length.. a week to weeks. What helped me the most was one, try and find ways to reduce stress, NO hot baths/showers (heat makes the hives worse) as people noted. try cool baths with oatmeal, BUT beware, the chlorine in the water (warm or cool)can dry your skin out and further inflame the hives. Additionally and what I found of most importance, DO keep hydrated with water .. Keeping your body well hydrated will allow your body functions to more readily combat the hives. If you are like some pregnant women, because once we drink something, you readily feel the urge to urinate , we sometimes STOP drinking as much water as we may need.
Also, at first I took allergy medicine like benadryl, but I too found I was allergic to it and in fact, in the shortrun while that type of medicine might kinda work, in the long run, I think the adverse effects are much worse and harsh on the body (at least for me) pain in my chest, dehydration.. etc..
Mostly, I would make bathing very short and in cooler water because as mentioned, the chlorine in our water supply can , in my opinion irritate and further dry your skin (I do this anyway) regardless of not being pregnant... and drink plenty of good water...I think these two will help. Oh and I personally, I wouldn't oil up your skin with too many lotions.. I truly think the hives will do better IF allowed to breathe.. especially at night.. wear cotton clothing.. that does not cling.. You may have noticed, once you are in bed, the heat of the blankets/body heat can eventually warm you up so much that it triggers an itching spell..... again, let the hives breathe....