Honestly, without seeing it clearly it's really hard to say what kind of rash it is, and since it has been there for a while without shrinking, I think it would be good to bring your little one to see the PD just to be safe. A few of my mum friends had similar situations where the rash looked mild but the PD identified it straightaway and gave the right cream for it. Better to get a proper diagnosis than to keep guessing, especially if it is not going away on its own.