What Causes Red Bumps On Neck, Arms And Feet?

A few months ago I had a terrible reaction to coming off predniose. I was violently ill, dizzy, couldn t concentrate. I am getting better but it has left me with large red welts on my body especially around my neck, arms and sometimes my feet. My doctor does not know whats wrong, this has been going on for three months and I am at my whits end.....help