This could be so many different things - eczema, dermatitis, an allergic reaction to something, among a lot of other things. Unfortunately, we can't diagnose you, since bumps can be so many different things. You should go to your doctor and get it checked out.
The next time you get this, call your doctor and explain that you need to be seen promptly because these symptoms disappear within a week or so. Take pics, too, so they can see it if there are any changes to them during the week they are there.