Me too - exactly the same. Drove me insane for years, but oddly seemed to happen only during summer months from, say, about May through to Oct/Nov. Then eased off till the next year. I tried every OTC cream/lotion going, but no relief. Eventually went to gp, who sadly simply prescribed exactly what I had already tried
(they just don't listen do they!)
Eventually I found a temporary "cure" using cold water and ice cubes. That was the only thing that has helped me. When the itching started I found that rubbing an ice cube up and down my forearms gave me relief for a few hours. Obviously I had to keep towels and tissues handy, so not very convenient when not at home. Other times (like when at work or in a restaurant) I had to hold my arms underneath a running tap and that would work as well. Trouble was, holding your arms under a freezing cold tap at 2.o'clock in the morning isn't conducive to getting a decent night's sleep. But at least, I wasn't making it worse by the continual scratching, often to the point of making my arms bleed. Sadly, antihistamines didn't work for me, nor any of the creams I tried.
Like Chris mentioned above, I think that mine is related to higher bg levels and stress (though have no medical evidence for that opinion). I have learnt through experience that provided I keep my levels low-ish, I appear to be ok. Have only had a couple of episodes this summer.