I think you may have polymorphous light eruption. Don't be impressed--it's pretty common and annoying but not serious. This condition starts at some point (no reason, like all allergies), and represents an allergic reaction to the ultraviolet rays that mostly aren't blocked by sunscreen (UVA). It gets milder the more you're exposed in any given sun season. It isn't reated to any other allergy. Try a UVA sunblock (there are lots) and an antihistamine (Benadryl, Claritin.) Also see you dermatologist about confirming this diagnosis by exam or blood tests, if needed. I agree that prednisone is strong. If I'm right about the diagnosis, you won't need it again. Go and find out.
Take care.
Dr. Rockoff