Random Rash

I have developed this small rash where my panty line is on one side and under one of my arms. It is relatively painless and has a burning sensation occasionally, but not much. It will be lighter and become more red randomly. I work out everyday and tend to sweat a lot so I wasn’t sure if that could be what this is? Googling is not good because it has me crazy stressed.

Anyone have any experience with this?