I Have Been Struggling With A Rash On My Back

I have been struggling with a rash on my back for 4 years now on my back I take allergy medicine before I go to sleep because it for some reason my back itches more at night at first I thought it was a reaction to the beding or detergent so I switched to silk beding and was my beding with just water and still the same nothing seems to work and just until 3 days ago am getting random sharp like electrical pain in my back that last 4 seconds then disappears for a few minutes then hits me again and this is a new symptom for me and is scaring me