As weird as it sounds, I've developed severe hives as a response to mild respiratory infections several times. It's not as simple as being allergic to the virus. My immune system over-reacts to the virus and everything goes haywire. Even after I've recovered from the viral infection my immune system over-reacts to many things in my environment, as if I'm allergic to everything. I'm not. I have a few real allergies and when my immune system gets over stimulated, my body over-reacts to things I can normally tolerate.

Fortunately, so far, I respond to cortisone and diphenhydramine (Benadryl.) Too much diphenhydramine makes me loopy, bad memory, can't stay awake. Unfortunately, I need large doses to get the therapeutic effect.

I have several auto-immune illnesses. My body over-reacts to things that don't bother other people, like a small case of the sniffles. I feel fortunate that cortisone helps me. I also get a good response from strong black coffee and from generally trying to relax and stay calm.

I've had this response since childhood. Calling it an allergy to a virus is an over-simplification, a shorthand way of talking about it, but it doesn't really make sense. Some people have immune systems that can be triggered to over-react for weeks by a simple case of the sniffles or a light cold. The virus doesn't really matter that much. It's your immune system that's out of kilter.

Kiwi's suggestion to see an immune specialist is a good one, even if you saw a specialist in the hospital. You may need some longer term follow-up on an outpatient basis. I got the most help going to an endocrinologist and seeing my primary for regular follow-up.

I hope the hives clear up soon. But, yeah, like Kiwi said, get your immune system checked out.