Hives in the first trimester?

Melanie • Married since September 2014. Step mom to a beautiful 5 year old and soon to be mommy.
I'm only 6 weeks along but I have a bad case of the hives. Benadryl helped for a few hours but they came right back a few hours later. Anyone else have this? I haven't changed soaps, detergent, or anything recently. I know a doctor can't do much but I literally not allergic to anything so I'm worried. Any advice?