Rash That Appeared On Chest, Then Subsided And Appeared Around

Rash that appeared on chest, then subsided and appeared around neck, now on interior of arms (where bending) and back of knees. Developed last week while in high altitude for one week, where breathing difficult, headache, overall exhaustion. Rash is more of a prickly feeling, rather than itchy.
Doctor prescribed low dose of prednisone....on 3rd day and rash just seems to be moving around to different areas?