perivascular dermititis

My Doctor diagnosed a seasonal rash that I have gotten over the last several years during the summer months as Perivascular dermititis after he thought it was shingles and then he did a biopsy.  It seems to be mostly concentrated in the waist area and in the groin area but I have had break outs on my back thigh and foot.  It begins in July and ends by October.  I have tried topical steroids which help with the itching but they seem to last for about a week to a week and a half.  I am convinced that this is some type of allergy and last year I had success by taking claritin every day.  This year it doesn't seem to be working yet as I start taking the allergy medication once I get my first breakout which was fairly bad and spread out on my hip with about 15 blisters rather than the usual one that I get.  It does seem to be healing now.  Does anyone out there suffer from something similar to this?  Is this something common for others and we just don't talk about it?  I have a history of autoimmune issues.  I like swimming in the pool at the beach in the ocean.  I live in New England.  Perhaps there is a trigger I could be missing.  Thanks for any help.