What Causes Red Itchy Bumps And Rashes On Lower Back?

For about 6 weeks, I have had on and off red, itchy bumps and small patches of rash. It started on my lower back, then a patch on my left shoulder, then on the left side of my neck. Now I have a lump the size of an egg on the left side of my neck, and a rash that covers most of the front of my shin.