Is this a sun rash?

I have very fair skin and blonde hair. I've always had sensitive skin and could never tan (just burn), so I stopped trying many many years ago. I had 2 cases in my life of sun poisoning from being out in the sun for only a few hours, one of those days it was cloudy. Other than that, I've never had any other problems, until now.

This year, I notice that whenever I spend the day outside, even if I'm not constantly in the sun, I develop a rash on my arms. Itchy, small red bumps, some of the bumps look like they are small blisters and when I scratch them some break open. It always develops in the evening, a few hours after I've come home from being out. I've never had this problem before. The only life changed I've made is that I had 2 kids, and I live in WV in the mountains, where the locals tell me the sun is stronger here than at sea level.

Is this a sun rash? If so, why did it develop suddenly?  I'm 33 years old and I try to take care of my skin as best I can. I don't seem to get this rash on my face, just my arms. I don't wear shorts so my legs are not exposed to the sun.