Is Rosella, Related With Rashes On Torso With Temperature?

My 2 year old boy has a rash on the right side of his torso and right arm. It started out as red spots, but they have now clumped together and spread.He did have a higher than normal temperature and was generally unwell for 2-3 days before the rash came, making me think it was Roseola, but the rash has been there for over 2 weeks now.Photographs can be provided.