itchy bumps very small and itch like crazy !

I get these itchy bumps on my skin that come and go. They sometimes show up on the side of my hips, inside of my wrists and/or my forearm near my elbows.. they. appear either very small to the size of a nickel and itch like crazy they appear out of nowhere and stay for an hour, maybe two. I notice them the most on the inside of my wrist. When I excersize.