"Bood Rash"

When I am on my feet in the heat doing a lot of walking, I get this blood rash on both legs which starts above the ankle and now reaches almost to my knees. The rash is worse on the inside and back of my legs, but then gets around to the front. It usually does not get to the outside of my leg. It is very red and smooth (no bumps) and it doesn't blanch when you press on it. It doesn' itch or burn but is very uncomfortable because of the tightness of the skin. Depending on the severity, it may take about five days to go away. It turns brown after a couple of days and slowly fades.
Can you tell me what this might be. It never occurs when the weather is cool and I am on my feet a lot.