Is it the types of flowers you have? Bees build hives where there is a source of pollen ... http://www.telegraph.co.uk/gardenin...pring-flowers-and-plants-to-attract-bees.html
On a serious note, I get hives as a reaction to some drugs (blood pressure and penicillin), and when I eat wheat/gluten and lactose, but without any medical training, or knowledge about you, its a near impossible question to answer I'm afraid.