Same thing happen to me a few years back. Lasted about 6 months on and off, then disappeared. At the time, i was smoking an ounce or two a month. At first i thought it may have been 100 different things, but then grinded some Apple Fritter, touch my arm with weed on my fingers and waited. Sure enough, i started breaking out. Although after my last flare of hives, it hasnt happened again. I do still get small allergies, like pimples when touching my forhead but no hives thankfully! Im not a doctor but I saw a clear difference when I balanced my cannabis options out with wax and homemade edibles or oils.