I don't know what's on my arms please help.?

For the past 3-4 days I have been getting these tiny red bumps (some are clear and I had a deep red one) on my arms that are itchy and then they disappear and then I find more some other place on my arm.! They are really only on my arms.! They disappear a lot and then reappear.! If you have any ideas on what they are please tell me.!