A doctor would have to see it for a diagnosis.
There are cases were it could be ring worm. Or it could be just due to sweat or sensitive skin. If it getting larger and in a circle, i would see a doctor.
You could be prenant. Go to the doctor to find out why your peeing so much. You could have a infection or you could be pregnant. You need to wait till your period is a few days late then do a pregnancy test