I Have Had A Dark Spot On My Arm Since

I have had a dark spot on my arm since Dec 2014. It started iut as what felt and lookd like a bruise. Then it began to flake and the skin became very dry and itched. I peeled it off. Now, every so often ...like today.... ut is covered by a raised bright red apot that is itcy and hot to the touch. I am also a severe urticaria patient. In addition, a smaller spot has now come up on my neck. What could this be from?