What Causes Rashes On Forearms?

I have a terrible rash on forearms and random places. I thought it might be bedbugs because it has that line effect in most places. I can't find any evidence of bed bugs. Sheets are always clean and I even put double edged tape around top edge of mattress and that was clean nothing stuck in it. Could it be scabies. Am itching terribly and have no clue what it is.