Localized itching with blisters

[sandy38]

I experienced this intense intermittent itching on my upper arm though there is no redness or bumps. Within a couple days red raised bumps followed by scabs appear that are wildly itchy.  These bumps then open with crater tops and a yellow fluid leaks out.  It takes weeks before the itching stops.  I had this last summer as well; never any other time of year.  I'll get occasional ones on my other arm.  Since it's so localized it seems like a contact reaction but considering there is never any change in my skin when the itching starts I'm baffled.  There are probably about 1/2 dozen of the open lesions there now without any redness around them.  Any ideas?

[purple1234567]

It could be an allergic reaction of some type to something you are only exposed to during the summer.  Have you made it to a doctor to have them look at this?