I Have A Rash From Time To Time That Seems

I have a rash from time to time that seems to mirror on the other side of my body. Example: starts on left ankle, will also show up on right ankle. I am currently experiencing this rash on a larger scale on my upper thigh that is increasing and moving. Once again, the same rash going on in the same area on the other leg. When I have had this in the past, It usually is only present for a few weeks, but I would certainly like to avoid it all together. It does itch some, more when it is hot and damp. Any suggestions?