it could be a ringworm-a type of fungal infect. if it has a raised outer rim that is a little darker red than the center-do u have cats or other pets, or do u work/go outside alot in the dirt or soil? IDK for sure but they can look like tht and they sometimes will not change that much if u leave them alone. My grandma treated them with the green peelings of Walnut tree walnuts and they would go away on us kids-we were always outside and into something as kids=)
Have you been to your doctor to have this looked at? It could be nothing but it could be something, especially if you have been exposed to the sun more than usual.