Have you been outdoors in a woodsy area recently? One of the first symptoms of Lyme disease (which is transmitted through deer tick bites, so tiny you'd never notice them) is a ring-like rash. If you think that this may be a possibility, go to your doctor NOW and get tested for it. When caught in the early stages Lyme is completely treatable with antibiotics. If you let it go untreated, it can lead to permanent joint pain and fatigue, along with other unpleasant things.
I have no joint pain or severe fatigue. My only symptom is the oval ring rash on the side of my stomach.
Google Pityriasis Rosea, may be a possibility