Pregnancy allergies??

Lacey • Baby #3 will be here July 8th! (Due the 15th with scheduled c section)
I only get allergies to peanuts when I'm pregnant. I get hives. And itchy and it's weird. It takes about 3 months to go away after (had tests done) and then I'm fine and can eat all the pbj I want (I get horrible cravings for peanut butter now) 
I was told with my first it was a very common thing. And my second I was allergic to all tree nuts. But this is silly.. I thought I skipped it this time till I started with hives on my ankles that spread to my hips. 
Anyone else go thru this? I'm horribly allergic to pistachios,  Started when I was 18. I wonder if that's related?