What Causes Hot Flashes And Itchy Rashes On The Arms?

Hi I have been experiencing a lot of hot flashes for the last 2 weeks and then get cold. It happens like every 20-30 minutes. 2 days I got these large red hives that look like bite marks on my arm that itch. They are a size of a quarter and very red. There are 8 of them. What is this?