What Causes Red Itchy Bumps All Over The Chest, Arms And Back?

Hello! I have had an allergic reaction to something. I have little red itchy bumps all over my chest, arms, and back. I take allergy shots, & am on regulated cycle. I take Norco for severe knee pain, and I have had very minor itching sometimes, but nothing like this. Never had a reaction to the shots, either. I have been on the same dose for over two years of pain medicine. It doesn t look like anything I have looked up. Can you help?