This only started a few days ago.

I change situations, for example I enter from outside or get up from sitting or something that slightly changes my environment in some way, and suddenly I get an itchy rash on my belly chest forehead shoulders and back. This lasts for 30 minutes or so and gradually goes away. It is not a case of heat or sweat rash but seems to be tied to slight temperature changes. The rash is barely visible but itches like crazy.