well good news
if you were posting 2 hours after the original post, and still slightly worried, then it's not flesh eating disease, you can litterally watch it spread over your body
I was tested for it when I was in grade 9, turned out to be
cellulitis. If that is the case, don't worry, go to the doctor/ER (if it is that, they won't say it's nothing as it can be serious if untreated, but it's a simple IV a couple of times over a few days to clear it up, followed by some medication in pill form).
Just to be clear, I am NO doctor by any stretch of the imagination. But I'd get it checked out sooner rather than later.
Hope it's nothing but a coinsidential heat rash.